Why do people hate uncertainty?

People prefer the things they know over the things they don't understand as this can help them feel safer (See why we like familiar things).

When a person becomes uncertain his mind might start to think of the possible bad events that could happen. Uncertainty thus could lead to bad moods.

People who always want to be in control of everything usually hate uncertainty since it takes control away from them.

Investors usually move away from uncertainty by putting money in asset classes that they are certain about (See also the psychological factors affecting the stock market).

According to a theory called the Zeigarnik effect the brain keeps thinking about issues as long as there is incomplete information. Because uncertainty usually means that there is incomplete information it can result in unpleasant feelings.

Many people fear the unknown and when they become uncertain about something their fears grow bigger.

When a person becomes uncertain about something that he cares about he starts to become anxious. some people hate uncertainty because it brings anxiety.

When people become uncertain about something the possibility of spreading a rumor becomes much higher.

When they become uncertain pessimists might start thinking about the worst possible scenario.