Source

Over-confidence
80 percent of people think they are above average at driving a car. Is it also 80 percent of people thinking they got a special gift to beat the market?

Fear of regret
Not able to sell with a loss, and keeping a loser for years.

Following the crowd
It is ok to lose money as long as the rest of the crowd is also losing money. It may be less embarrassing to lose money if everybody else is also losing.

Sticking with the status quo
If you were starting out investing today, what stocks would you buy? If those are totally different from the stocks you are currently owning why is it so?

Short sightedness
Putting too much weight on the recent past. After a bad market, they overestimate the chances of another bad year.

Seeing patterns
Quote: “It’s often useful to see patterns in data. Sometimes, though, people see patterns in coincidence. Around the 1929 Wall Street crash, for example, observers noted a close correlation between New York and London share prices and levels of solar radiation.”

The frame-up
The same information can be presented to look good and to look bad.
Quote: “People respond to how things are framed. They don’t like an investment that has losses one year in 10 as much as one that has gains nine years in 10!”

Selective listening
It is often very comfortable to have pre-judgements confirmed.