Bravo, stranger! You could say that the latter begets the former. Being able to follow a trend means you've got enough power, capital, and social awareness to afford keeping up with constant change, all of which are valuable markers of status in many societies. Being fashionable is a neat way to claim ownership over all three.

And by being fashionable, different social groups open up to you as they recognize you as their own. Once you're in the group, you can choose to absorb their social culture or introduce new ideas, forming a different trend within the group that can spread to many other circles. And so on, and so forth.