Comment by billforsternz

The process of converting a completely winning position (typically one with a large material advantage) is a phase change relative to normal play which is the struggle to achieve such a position. In other words you are doing something different at that point. For example, me as weak FIDE CM (Candidate Master) could not compete with a top grandmaster in a game of chess, but I could finish off a trivial win.

Edit: Recently I brought some ancient (1978) chess software back to life https://github.com/billforsternz/retro-sargon. These two phases of chess, basically two different games, were quite noticeable with that program, which is chess software stripped back to the bone. Sargon 1978 could play decently well, but it absolutely did not have the technique to convert winning positions (because this is different challenge to regular chess). For example, it could not in general mate with rook (or even queen) and king against bare king. The technique of squeezing the enemy king into a progressively smaller box was unknown to it.