I would say when you start frequently playing games that rarely involve random (very obvious) piece blunders but instead involve tactical or positional blunders that are harder to spot for beginners. You also need to master the technique of very basic endgames like Q+K vs. K and R+K vs. K or K+P vs. K, learn the concept of opposition and stalemate, understand the opening principles and be aware of the basic tactical ideas like the pin, the discovered attack and the fork.
I would say all of this happens at around 1500-1600 rapid elo, at least id did for me. Random piece blunders still happens, but is much less frequent at that level.
The title is the question. Inspired by a similar thread.