A lone (or a few) rotten eggs in a basket...

Dunno (a.k.a. too lazy to search) who said this first, but:

A lone (or a few) rotten eggs in a basket makes it seem like a basket full of nothing but rotten eggs. 

Anyways, I think we can learn two lessons from this saying:


Lesson #1: try your best not to be a rotten egg!

Lesson #2: let's not judge the whole basket if you haven't yet checked all the eggs in the basket.

I think #2 is easy enough, except when you've mistakenly thought that you've actually checked all the eggs in the basket.

#1 needs constant effort -- it is not easy. Even if you've done a lot of great things in your life, all it takes is one mistake (one rotten egg!) to erase it all. When we encounter people who make that one mistake, we should refer to Lesson #2.