I have poker nights with my buddies, and I try to play ice hockey every once in a while. All this requires a delicate balance of planning out the work. The research is a top priority, but my sanity is definitely at the top of my list. A big issue to many graduate students is keeping focused on the research. The focus can be maintained by being constantly motivated, and that may be somewhat hard.
All projects have high points and low points.
My P.I. once told me, You will try a reaction 100 times. Out of those 100, you will most likely fail 99 times. The one that counts is the one you get to work. Failure is a big part of the learning experience. The most frustrating years tend to be the third and fourth years.