It also depend on which type of game it is. If its a 1v1, or team vs team its often easier to know that its over. In a FFA others might battle while you can grow an army even if you don't have much.
I have a fun story in this topic. One of my best friends (called multimarine) was a very hard core starcraft player. At one point he went to South korea on a big tournament (Starcraft is a national sport on TV there with sponsoring, huge prizes, super star status if you are good, compare it to the most popular sport where you live and you know.).
This was when it was getting big in Korea so they had a big tournament and they would fly the best starcraft players from outside Korea to go there and join the tournament. My friend was at his prime and went there to play.
I don't know how many players he had beat when he got to play a guy from Canada called Grrrr.. Grrr was considered the best starcraft player outside Korea by most hardcore players at the time.
In this game my friend plays grrr and beat him, or actually he manages to kill off all his units and income and have a bunch of marines in his base so grrr says Good game (mean he considered it a loss). But he doesn't press surrender and my friend removes his marines from grrrs base and sit back in his chair relieved after a intense game. It doesn't take long before Grrr manages to have the weapon he was working on finished that is nearly impossible to kill with marines. I don't know how long it takes before multimarine realizes that he haven't won yet. But suddenly grr attacks with some last desperate try and manages to kill the marines with his new weapon and then win the game.
Grrr then went on and won the tournament got a sponsor contract and becomes the number one pro player in Korea for about a year making lots of money, girls and fame (its not everywhere you can get girls by being good at a computer game
).
I don't know how many times we have said to multimarine ARGHHH how could you remove your marines and not continue until it was 100% over (and I wonder how many times he thought about it). Since that day when I'm losing or winning that story echo in my head telling me to not stop before its over
.