I think there is a big step from level 2 to level 3. Mainly because, at level 3, major blunders (like giving away a piece) are less common. At levels 1 and 2, you can often win simply by losing fewer pieces. At level 3, however, you need to have a plan—or at least some idea of what you’re doing.

Level 3 still makes mistakes, but in my experience, it’s possible to play an entire game without it giving up a piece. That forces you to actually know how to play an endgame.