[ Repeat ]

Skills develop through repetition and practise. This especially applies to technical skills like calculations and problem solving.  Solving something once, even done well that one time, doesn’t mean you’re skilled at it.  

We’re not “skilled” at something until it is second nature, or a habit.  It’s a skill when, for example, a problem to solve comes up and you don’t have to think about how to solve it, you just do.

The problem with advancing quickly through a career, is that there’s little opportunity to practise, or repeat, a skill, after demonstrating it once.  Developing skills takes time.  And repetition.