Updated April 17, 2014
People love the little things in a product. They also hate the little things.
A car is a miracle of modern science, but people like how the door shuts or how the headlights are cool looking. A person is complex, but we judge their handshake.
The psychology is that people can’t deal with the totality of something complex. They zoom down to a detail to make an easier judgement call on quality.
So if you are building a product. Think about the little details. Make sure to put a few things to love down in there. Learn about the little things users hate, hate, hate and fix those little annoyances. They usually are easy to fix but have enormous impact.