Ratings: 3 stars vs 5 stars. Why 5?

It's the most common interface used to display votes is the “star rating system,” in which a particular number of points (often expressed as stars) is assigned to an item by each reviewer. We find this model on many sites, from Amazon to Yelp. Stars seem like a pretty straightforward mechanism, both for your users to consume (5-star rating systems seem to be everywhere, so users aren't unfamiliar with them) and for us plan.

But 3 stars, for making a decision, I think give better insight to the consumers vs 5 stars. But what is the physcology behind the number 5 in ratings? Why not 3?