It's a common theme in stories, movies, whatever: have a single character that does pretty much everything.
Personally, I think one interesting way of looking it is to compare Half-Life 1 and Half-Life 2.
In HL1, we had a standard character, who was thrown into a situation (partly) of his doing and suddenly had to fight, at first just to survive, then to help others, then to help practically every survivor in Black Mesa, then possibly the entire Earth. It handled the situation very well, you always felt like you were just playing a role in what was happening, that there was multiple stuff happening elsewhere and many people around you doing different things (sneaking past grunts fighting aliens enforced this feeling). Because you gradually moved on from one task to another, it never seemed overwhelming and the gradual structure of the game made it feel like you just happened to be thrown into the central role by circumstance by eventually doing one of the most important things that needed to be done.
Contrast with HL2, instantly you're in an unseemly place, and suddenly, assumes you to be a great hero. In HL1, people didn't seem to take much note of you until pretty far into the game when you'd done a lot of worthy things, and even so, they seemed more surprised that you survived rather then enamoured with your great skill and prowess. However, despite it being unlikely that that many people would have heard about your exploits in the first place (Black Mesa was pretty hidden away), all the rebels suddenly seemed ready to fight with you, and give you stuff. What's more, it seemed a lot more contrived in being brought to the forefront of the rebel resistance. In HL1, it seemed you earned the reputation through fate, luck, determination, and circumstance; in HL2 you were instantly assigned the role of a hero and suddenly expected to live up to it.