more or less general, but started as a response to banjocat:
It has more to do with being able to work your ass off, have thick skin (tolerate other peoples opinions, tolerate the general public), have strong convictions and dedication, generally be a hard worker that is self motivated and it helps to be resourceful!!!
Otherwise, there is no being qualified, you sink or you swim, handling 100 tanks or 500 tanks is about dedication, organization, persistence, adaptability, etc....
oh yeah, staying humble helps too, you have to be able to accept the fact that there is always more to learn, this is where I stumble the most, when I assume I know what I am doing and make a mistake.