It depends on a lot of things. What sort of riding have you been doing? Are you doing it as a competitive sport, or just for fun? Are you actively not liking the riding you're doing, or is it that you've gotten to where it's not a challenge, and you want to try something different for a change?
That last has always been something that has affected me. A big part of the pleasure I've gotten from a lot of the activities I've done throughout my life has been the learning process, the acquisition of new skills. So once I get fairly good at something, my interest tends to taper off because I find some new challenge.
But don't overlook Marecare's advice, either