Boring AND conceited. I always roll my eyes at this trope of "unlike all these different fantasy beings that are good are specific things, we can be good at everything". Seems like imagination falling short, that other beings would not have their own breadth of possibilities, and humans wouldn't have their own unique advantages that are particular just to them.

If I had to pick one thing, it would probably be something teamwork related. Humans are very social beings compared to other animals.

Especially given humans have real standout traits like being endurance hunters, somewhat rapid scarring and a high resistance to shock (advantage on constitution checks?)