Is it a good idea to play unusual openings (openings except d or e file) (like c4, played by Bobby Fischer on the game of the century ) to confuse the opponent and stop him/her to play his/her natural opening (like Sicilian, Pirc defence etc.) in the rated tournaments ?
Absolutely! This is an important component of opening preparation. If you know your opponent is very booked up in e.g. the Sicilian Najdorf, entering the Sicilian Najdorf is suicide unless you also have specialist knowledge. You are liable to be caught in an opening trap or make otherwise inferior moves against which the opponent has memorized the best responses. Game 1 of the World Chess Championship 2010 is illustrative: Anand forgot his preparation and when Topalov responded instantly, Anand knew at once that he was lost. More to the point, he didn't actually lose the game to Topalov's superior chess, he lost to Topalov's computer & memory.
In a similar way, if you know your opponent likes tactical melees, playing for closed positions where slow maneuver is the order of the day can dramatically increase your win rate against him. Directly challenging the opponent in the area of his strength is fine if you're looking to improve, and not so fine if you just want to win.
In case you're wondering, the same principles apply as well in the highest level of play: correspondence chess. To quote from an interview with the then-world correspondence chess champion,
It is indeed impossible to achieve any significant result in today’s correspondence chess without engines and databases. But we humans play, not the engines, and the input of humans mainly affects two areas: a) the choice of a suitable opening, and b) steering the engine toward (or away) from certain types of position.
If you want to be successful in top correspondence chess you can only play a certain set of openings because you simply cannot afford one single sub-optimal move – if you do, you will sooner or later regret it. That’s as certain as death and taxes.
I used Rybka for a number of years but around 2012 and 2103 I switched to Stockfish. Of course, I tested other engines as well but these two are my main engines. I firmly believe that the top CC players must not change their engines too much because you have to understand and recognize the strengths and weaknesses of your engines. Otherwise, you again and again have to choose between two or three moves the engines suggest, however, without understanding the differences these moves.
If your engine is good at positional play, those are the positions you want to gun for. If you further manage to identify the opponent's engine is not good at positional play, more power to you if you successfully get into such a position.
There are many ways of looking at this depending on one's strength. Super Grandmasters are able to shift between openings with ease and still play them well at a very high level and with deep understanding. As for middling players, it is good to stay with one opening line for long and there are several advantages to that;
- Experience is a very important aspect in the road to mastery and there's no shortcut to acquiring experience. The great martial artist, Bruce Lee once said,
I fear not the man who has practiced 10,000 kicks (chess openings) once, but I fear the man who has practiced one kick (chess opening) 10,000 times.
The same could also be said about chess and sticking with one (or a few) opening lines for long time, acquiring more experience, deepening your understanding in strategic & tactical ideas behind the opening and both the resulting middlegames and endgame positions.
- Don't play against the player but play against the pieces. Most great masters of the past including Bobby Fischer himself have stayed with one opening repertoire for long and playing fearlessly against all their opponents. Fischer played just a few openings, Ruy Lopez, Sicilian Najdorf, King's Indian Attack & Defense, Grunfeld Defense, and others in between. Some openings and variations have been named after masters simply because they remained loyal for long and built indepth understanding in those lines.
- The desire to win quickly and the creeping in of last minute doubt in one's opening repertoire is what has led many players to run away from their main weapons, hoping that the new unknown opening will yield better results in their favor. More often than not, it is the same players that end up surprising themselves with their own lack of experience in the new unusual opening than surprising their opponents. The sad is thing is that after the game, there isn't much to analyse or to add to your experience in that surprise opening.
For serious tournament games, I would strongly recommend sticking with one's main opening repertoire and using surprise openings for blitz and casual chess. As for beginners, I would recommend that they should stay with simple openings that adhere to basic opening principles (develop your pieces quickly, knights first, king safety, etc) like the Italian Game before trying to surprise anyone.
First, I'm not convinced Fischer's 1. c4 was the masterstroke some claim. His Bb5 had already been played by Furman against Geller, one of Spassky's seconds, and was nothing special. (As shown the next year when Timman ventured that same line against Geller, who responded with the continuation he himself had shown Spassky during the match prep and won.) I think Spassky had already been rocked back on his heels before Game 6 by the way Fischer responded to being two games down -- drawing even by winning his next two games as black. Starting with Game 5 Spassky became uncharacteristically blunder-prone for a fatal stretch. I'm not sure the end result would have changed had Fischer simply stuck to his e4 habit. (See for example, Game 10.)
As for the main question: I've always encouraged my students to experiment with openings, for the simple reason that until both players have reached a basic level of strength (it's an uncertain line but it's somewhere north of USCF1800) specific opening choices really don't matter, and it's a way for them to discover what kinds of positions they like to play and have a natural aptitude for.
The unfortunate truth is for beginning and club-level players, the propensity for making errors in the middlegame and endgame will more than offset any advantage gained by memorizing a list of opening moves.
The question why I wasn't telling them which openings to play came up in a training session with one of my high school teams, so I opened my scorebook and we took a look at all the rated tournament games I had won so far that year (15, I think). We discovered that in all but one of those games I had come out of the opening behind, ranging from standing a little bit worse to being well on my way to losing. (I've long had a propensity for playing oddball lines, just to see how they play out against humans, rather than computers.) Yet I'd won, mainly because once the game shifted gears into the middle game or the endgame, my opponent didn't know what to do.
The first things to work on are calculation/visualization and basic endgames. Basic principles of chess, such as mobility, development, and control of the center. Go ahead and try out different opening lines, with the aim of figuring out whether the resulting positions suit you, not because of some supposed psychological effect on your opponent. Until the rest of your game is good enough to hold on to an early edge, none of that will matter for you. (If you want to play some trappy line and hope your opponent won't find the right path through it, go ahead. But remember, winning via memorized book traps says nothing at all about how good you are at chess, only how good your memory is.)
Specific opening preparation can wait until you're good enough to hold on to the advantage that preparation might give you.
Anatoly Karpov spoke at one of Scholastic Championships I brought a team to, and one of the coaches there asked him to comment on what US coaches were doing wrong. You could see him think carefully for a while (since his English is quite good, I personally think as a gentleman he was trying to find a way to say it clearly without offending his hosts) "You think too much about the opening. First comes chess. After you play it well, then is the time to think about openings."
You want to play some offbeat lines? Go ahead. Have some fun with them. Experiment. Dance with the wallflowers of chess opening theory. But unless both you and your opponent are dancing with candidate master or better skill, don't do it for any sort of opening advantage, because the odds are you'll give it all back before the game is over.