Base of User Experience Design comes from understanding of the human psychology and how/what affects people’s decision making. Predictably Irrational by Dan Ariely is one of my long overdue reading list and I finally had time to go over it. It covers lots of elements that can be very helpful in UX design and I’d like to summarize the book by the 9 key points.

Comparison: People always want to compare to get the better deal. The best approach is that give 2 very similar options to choose from but one slightly less desirable so people don’t have to think too much.
Social norm vs Market norm: Every action is either part of the Social norm which is a warm, friendly, no payment required requests or the Market norm which is a cold, calculating, resourceful, selfish requests. We have to be very careful when take an action since reverting from Market norm to Social norm is hard.
Power of Free: Free is not just a word but more of the irresistible emotional trigger. When something is free, it has no risk or a downside of ‘losing’ which people are always afraid of, and the free becomes more valuable to them (called Zero Price Effect).
Fight the procrastination: To have the rational long-term goals and fight the irrational urges/procrastination along the way, its important to know our weaknesses and set the hard restrictions/deadlines in a broken down short terms.
Owning: When you own something, we tend to overvalue it because we fall it love with what we own. Therefore, we expect other people to appreciate as much as we love.
Options: People always want to have other options open even though they choose one so [...]