Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
To make that position reachable, black must previously have had the queen on h1 and just captured a white pawn, knight or rook on h2, which then starts the forced sequence.
1. a4 does not force the b5 pawn to choose between capturing or being captured: black can also respond with ...b4 (push past it). But that does then hinder the advance of the b6 pawn.
No it's not hard to lose against a random player if you want to lose. You can try it with the Play Magnus app set to 5-year-old. You just have to force a situation where the only legal move it can make is to deliver checkmate. The easiest way to do this is capture all its pieces except 1 pawn, trap its king so it can only advance the pawn, leave your king on the first rank and arrange your other pieces to block your king from escaping when the pawn promotes and calls check. This works if it promotes to queen or rook, so you have a 50% chance of losing (or 100% if it never under-promotes).
