At least two very different for me:

Myst: I was very small when I played it so maybe I missed some slightly hidden warnings or foreshadowing. But basically during the whole game two brothers that are trapped in two magical books claims that the other brother is evil and trapper him in this books.

It looks like the only way to progress in the game is to trust one of them and go do the quests they are asking in order to free them.

I thought I was smart and did everytime both quests for each of them, my plan was to save before the final quest of one and check if is the "good" one, otherwise reload and finish the last quest of the other.

I finish one guy. cue evil laughter I finish trapped in the book and the evil brother laugh that he managed to lie to me for this whole time. Fine, let's reload 5 minutes ago and free the other one. another evil laughter basically same thing happen with the other ... wtf ? There is no good ending to this game ??

Turned out there was the dad of this two also trapped in another book that was hidden somewhere else, he was the real good guy and lead to the good ending.

So: don't trust anyone, always look for more options than the two obvious choices that are only an illusion of free will. Lesson learned at a young age.

Other one that is more coming from the community than the game itself: world of Warcraft (vanilla, when it get out), more specifically beating the end boss of the latest raid for the first time. Especially when you are the raid leader. It give such a satisfaction and sensation of fulfilment.

There are a lot of games that require a lot more personnal skill than WoW to beat a boss. But getting 40 people to be ready, prepared, have to good class and good equipment, and play together for hours in order to achieve this common goal is incredible.