I have seen this in the time that I have been backpacking for many years time and time again. I will admit that I am guilty of it myself when I was starting out as a budget-traveler. I was still guilty of it after years of being in the "game." I do not make this mistake now because I know that as a backpacker, chances are you are going to a place that has a lower economic standard than where you are coming from.
This it the privilege that we in any Western countries have, at least for now and while that socio-economic situation is a conversation of its own it is not one I am trying to have right now. If you are able to backpack or do a gap year, you are part of the privileged few and well, that is great.
In the meantime don't be an idiot and bring a bunch of gear that you are probably not going to use and even if you did need it you can almost certainly get it cheaper at the destination than you can by bringing it along with you. I start with some of the things I have noticed over the years that everyone seems to make the same mistake on.
src