How do you cope with illness that has no time limit?

I'm talking about health issues that have no apparent cures, but time itself. How do you mentally arm yourself and cope when recovery may takes months, years, or more? How do you keep yourself from eating junk food, going to sleep late, or other destructive behaviours that temporarily subdue the pain? Do you have the attitude "Just deal with it!" or do you just listen to music? Looking forward to your replies!