If owning stocks is a long-term project for you, following their changes constantly is a very, very bad idea. It's the worst possible thing you can do, because people are so sensitive to short-term losses. If you count your money every day, you'll be miserable.
The concept of loss aversion is certainly the most significant contribution of psychology to behavioral economics.
A person who has not made peace with his losses is likely to accept gambles that would be unacceptable to him otherwise.
Negotiations over a shrinking pie are especially difficult because they require an allocation of losses. People tend to be much more easygoing when they bargain over an expanding pie.
People just hate the idea of losing. Any loss, even a small one, is just so terrible to contemplate that they compensate by buying insurance, including totally absurd policies like air travel.
When people think of the outcomes of their decisions, they think much more short term than that. They think in terms of gains and losses.