Not a quote, but a poem I also learned from the MBSR meditation workshop I took. I think it's fairly famous:
The Guest House
This being human is a guest house.
Every morning a new arrival.
A joy, a depression, a meanness,
some momentary awareness comes
as an unexpected visitor.
Welcome and entertain them all!
Even if they are a crowd of sorrows,
who violently sweep your house
empty of its furniture,
still, treat each guest honorably.
He may be clearing you out
for some new delight.
The dark thought, the shame, the malice.
Meet them at the door laughing and invite them in.
Be grateful for whatever comes.
Because each has been sent
as a guide from beyond.
--Jelaluddin Rumi