Here's a way of looking at perseverence in meditation that I hadn't thought of before:
Meditation will only be of limited benefit to you if you practice it on-and-off. The key to success in meditation is the commitment to meditate once or twice every day. Like embarking on a new career with a new employer: if you turn up for work only when you feel like it, you are unlikely to go very far in your career!It makes so much sense, doesn't it?
I found this on a page entitled "Advanced Guide to Meditation".