#1 It's hard, no matter how good you are
Unlike with some other majors, studying any natural science truly is a long and difficult task. It's not something that will happen overnight and will certainly take a lot of effort on your side, unless everything comes naturally for you.
#2 Non-STEM students won't understand your journey
I honestly didn't realise this until recently - I have more to talk about with my friend who also studies a STEM subject than with the ones who don't.
Of course, not studying the same subjects isn't an issue, but it's interesting how much more you have in common when you study a similar science!
#3 You may miss reading about something and then getting an assignment on it...
This is definitely the case for me. I miss picking up a textbook, learning about a topic in general, researching about it in more detail and then summarising everything in an essay. I know, for some, that may seem boring, but at least for me, studying Computer Science hasn't exactly been too reading-heavy and I miss that.
#4 ... but at least, you have something to show for at the end of the day
This is really, really good. Nothing is more satisfying than being able to run a good piece of code after obsessing over it for a few hours or being able to admire a long proof or calculation. Just anything that delivers results will be good enough.
#5 People will always try to get you to solve their math, health or tech related problems for you
No matter what natural science you study, there will be a point in time where you'll be approached by someone expecting you to have all the answers.
This can be a little challenging, especially when you feel the pressure, but it's always okay to admit that you don't have the required knowledge :)