Peter Principle

Definition

The idea that employees rise to the rank just beyond their competency, as they are evaluated on performance to their current role and not their intended one — at which point they cease to be promoted.

Origin

The concept was detailed in the book The Peter Principle by Laurence Peter and and Raymond Hull in 1969. (source)

Everyday Use

This is a good term for someone who works around coworkers everyday -- a reminder of its use hardly seems necessary! Yet this reminds us that no system is perfect -- almost everything we interact with, be it a coworker, or software, or process, or tool -- is 100% perfect, or even 100% for that job.