One of the things I'm struggling to adapt to with trumpet — even more than horn — is the incredible air pressure needed to reach the high notes and the ridiculous volume achieved.
Part of the problem, of course, is practicing in a small room without sound treatment: I'm sure the volume I'm producing is perfectly normal as trumpet goes, but it sounds absolutely deafening.
I'm quite sure the brass instruments have the steepest learning curve of any instrument group I've gone for. The only classical instruments that don't give you any visual indication of what note you're about to produce. Easy to screw up — and loudly.