What are some hard truths you’ve had to accept since the day you started your PhD?

Question is the title. Also, how hard was it to swallow those hard pills the first time? Any coping measures you’ve developed to deal with them?

Context: I’m prepping to start out as an international student on one in a few months. I’m just trying to figure out what to look forward to.

Edit: Wow. I expected a few pills, but not so many. I’ll probably keep coming back to tick off what all I face during my program. Nervous but excited!