3 is a magic number.

Yes it is:

A ratio of 3 to 1.

Via Rainy Brain, Sunny Brain: How to Retrain Your Brain to Overcome Pessimism and Achieve a More Positive Outlook:

Psychologist Barbara Frederickson is an expert on flourishing and has been an advocate of finding ways to bring more positive emotions into our lives. In her research she discovered a critical 3 to 1 ratio, indicating that we need to have three positive emotions for every negative one in order to thrive.

And:

Frederickson has found out that if we really want to prosper, we shouldn’t try to eliminate negative emotions, rather, we should work on keeping the ratio at three positive for every one negative.Most of us, she has found, have two positive experiences for every negative. This gets us by, but it is effectively languishing.

How many people are at 3 to 1? Around 20%.