Very rarely, a hero has to associate himself with other heroes to fight a threat that is impossible to beat alone. Any other time he faces one of those threats, he'll still choose to do it alone. Because if that threat is clearly easier than the others, so why wouldn't he call some of those more powerful guys? Absolutely pure ego. Millions of lives are put at risk three times a year because they don't want to pick up the phone and call Iron Man. That's right! Iron Man would have killed the Winter Soldier in exactly twenty seconds. TWENTY SECONDS!!! And that is just how long it takes to find the guy out there.
