Since being promoted to head of department, I spend much less time interacting socially outside work with my team. After all – familiarity breeds contempt (zu viel Vertraulichkeit schadet nur).
This is a very old saying, it has been part of the English language since the 16th century. As well as the meaning in the above example, you could also use it to describe the way we start to take everyday things for granted, or how we lose respect for dangerous things if we do them very often.