Once acquired, the habit of worrying seems hard to stop. We're raised to worry and aren't considered "grown up" until we perfect the art. Teenagers are told: "you'd better start worrying about your future". If your worries aren't at least as frequent as your bowel movements, you're seen as irresponsible, childish, aimless. That's a "responsible adult" game rule.
To the extent that worrying is learned/conditioned behaviour, it can be undone. There are psychological gimmicks for undoing the worry habit. There are also obstacles.
There's a useful gimmick to help stop worrying (we've already mentioned it briefly in How to Avoid Responsibilities, but it's worth looking at in detail). You simply cultivate the habit of postponing worrying. Your mind becomes (re-)conditioned to not dwell on worries in the present.