Some Buddhists believe that all things are transient, that everything changes.
But since all things do, in fact, change, why would anyone waste time believing it?
The answer, for my money, is that belief is a bulwark and a defense and an encouragement. It implies doubt. The firmer the belief, the greater the doubt. Belief relies on and resides in the past but we all exist in the present: Isn't that enough to fire up uncertainty and doubt?
Some say that we should pursue our spiritual endeavors without doubt, but I think that this is just whistling past the graveyard, trying to deny or cover up what is palpably true. And the difficulty with denying doubt is that its rich potential is cast into the shadows where in fact that doubt is more deserving of a warm embrace ... it puts a fire under your ass ... to find out for sure whether something is true or not.
My teacher, Kyudo Nakagawa Roshi, once told me that "for the first four or five years (of practice), belief and hope are necessary. After that, they are not so necessary." He didn't bad-mouth belief or hope. He just recognized them as tentative means -- things that, where experience took root, were no longer so necessary. Why bother doubting (or believing either) that you can ride a bike when the plain fact is that you can ride a bike?
Everyone chooses a practice that they imagine (and simultaneously doubt) will make them happy. I chose Zen Buddhism and, given half a chance, would call the practice a good one, an effective one ... a practice that allays the doubt that hides within belief and hope. But there are probably a zillion other practices which are equally effective ... assuming anyone was determined to get to the bottom of things.
Pick your poison and never give up -- that's about my take. No one wants to live a life that is filled with doubt and uncertainty. Everyone wants to be happy. So which tool is the most useful tool? Belief and hope and doubt are very nice for a while, but then it is time to let the practice do the talking.
Ride your bike. Everything changes. And it's OK.