Biggest mistake people make when they start working out?

Biggest mistake people make when they start working out?

 Answer:  Somebody who has never been to a gym and never exercised should start to exercise progressively, like the running in needed for a new car.

It often happen that people think that they have to do a lot because of the wasted time, but it's wrong.

Somebody who exercises more than his body can handle will end up injuring himself, and will then have to quit fitness for a while, or forever.