It was the same with Schumacher: the need for the adrenaline rush, to push himself to the limit was always there. So without a Formula One car to race with he went on to do motorcycle racing and other stupid things, and obviously that wasn't enough to keep him happy, so he had a problem to sort out and returning to racing was his answer to the problem.
Niki LaudaTaking your first title is much more complicated and more difficult; it takes years of work - from go-kart to Formula One. The second comes more easily, because you've already got the experience.
Niki Lauda