It’s usually when I complete the story. I’m not a big into 100% games anywhere, unless in a rare occassion it’s worth it. In some even rare instances, I won’t be done with a game after I complete it, I think after completing Doom and God of War, I went straight back into a second playthrough on a harder difficulty setting. This is where New Game plus is greatly appreciated.
Most frequently it’s when I become bored with a game. It’s not uncommon for me to move on to the next game.
Most recently however, after getting to the end of the main campaign of RDR2, it’s real hard to go back for the epilogue and just pick it up again. I almost just want to start again and mop everything up properly as that character.
The game I’ll never be done with is Threes. I’ve had it on my phone for about 5 years now. Never came close to beating it. I think if I do beat it one of these days I may be done with video games for life…