How do people really improve at chess?
I often hear people say that any of the following will improve a player's ability:
- Doing tactics puzzles
- Playing more games
- Playing bullet games
- Playing longer games
- Playing correspondence games
- Memorizing openings
- Analyzing own games
- Reading chess books
Sometimes I hear a specific example like "I've been doing tactics puzzles since last year and it has improved my understanding significantly", and then I ask for their lichess name, and I check it, and their rating has been extremely steady for the last 3 years.
Often these kinds of suggestions seem at first to be anecdotal, but even anecdotes would be true. These are worse than anecdotes because they are not based in reality.
Is there some scientific study of GMs and their history to find out exactly the key points that made them great? Or some study of kids over time with different training techniques and comparison of rating changes to see what works and what doesn't?
As far as I can tell, the thing GMs have in common is that they all had strong chess coaches when they were kids and became very strong players by the time they were 15 or younger.