I like this quote: The Secret of Exercise:

"I’ll tell you the secret right now: you’ll have to force yourself to exercise—but only for 7-10 days. After not exercising for a while, you won’t feel like it. It may even be very difficult to get back into it. But after 7-10 days, your body will be trained and you’ll actually be looking forward to your exercise routine. Start with 15 minutes and increase by 5 minutes every day. Pretty soon you’ll be rocking along with everybody at the gym."