I don't know anyone who didn't find it difficult. It's very isolating work, especially if your research is in the humanities (at least in the sciences you work as part of a research team in the same lab, but in the humanities you're mostly on your own in a library or at home), it's very hard to switch off and leave your work behind at the end of the day, and you feel guilty if you're not working. If you don't have mental health problems, you likely will by the end of the PhD, and if you already have mental health problems, they will be exacerbated.

I'm okay now, but the last two years of the PhD were not easy (compounded by the fact that I was extremely worried my visa would expire, I would not be able to move to a different visa category, and I would be forced to leave my friends, my partner, and the country).