We're not born with a fear of failure but acquire it. Parents and school teachers drum it into kids. "Colour inside the lines," and, "do it like this not like that," are common phrases that contribute. People are taught to conform and then as adults they don't know much else and so simply continue - I speak generally of course.

Common sense is one thing yes, but that's not the only reason people use to stay in place, there themselves or inhibit their own growth. There's a lot of excuses for lack of progression...most are just bullshit though.