Character Analysis
Coulson, like the Black Widow, is a loyal SHIELD operative, a guy who routinely does his job without a lot of fuss. He's meek and calm and almost preternaturally bland: in short, he's the last guy in the world you'd notice.
And that's kind of the point.
Coulson acts as a stand-in for all us normal folks: the ones without superpowers who have to believe in these heroes to stop forces that are beyond us. As such, the heroes ultimately owe him for standing in for the normal people they're trying to protect. He also reminds everyone that it starts with the little guy.
After all, he ultimately sacrifices himself to try to stop Loki, and while he fails, his willingness to put it all on the line really moves the heroes. He even wraps all his ideology into a few choice sound bites that he throws Loki's way before meeting his untimely end:
PHIL COULSON: You're gonna lose.
LOKI: Am I?
PHIL COULSON: It's in your nature.
LOKI: Your heroes are scattered, your floating fortress falls from the sky... where is my disadvantage?
PHIL COULSON: You lack conviction.
When our champions falter, it's up to us to remind them what they can do. That's Coulson to a "t": just a normal guy who just so happens to work with some extraordinary ones.