I thought that if I was visibly tired, busy and over-worked then that would somehow justify the importance of my work to the external observer. But taking time for yourself isn't a sign of weakness.
You’re only doing a PhD so you can be a student forever
If you get comments from people doing "real" 9-5 office jobs in "The City" about how you're "putting off life" by doing a PhD, you're not alone.
It’s okay to have nothing to say
After I started my PhD, I realised that it’s okay to admit you haven’t heard of X concept or X canonical text. This may sound obvious, but it wasn’t to me until I sat in my first PhD working group.