I have a couple of favourites to lighten the load:
"The only way to find out how to do a PhD is to do one. Therefore all advice is useless". I found that one googling 'how to survuve a PhD'
Lewis Carroll had some great advice for Alice in Wonderland "Begin at the beginning and go on until you come to the end; then stop."
Another favourite is atribbuted to Ronald T. Azuma:
"Being a graduate student is like becoming all of the Seven Dwarves. In the beginning you're Dopey and Bashful. In the middle, you are usually sick (Sneezy), tired (Sleepy), and irritable (Grumpy). But at the end, they call you Doc, and then you're Happy." Cheers, Anna