Realizing that I was over 40, fat, and out of shape did it for me. The first rides sucked but it gets better fast. Concentrate on how fun it is, not how slow you are.

Even now that I am racing there's some days, usually in winter, when I find it hard to get out. When this happens I tell myself that I'll just go out for a half hour. If I still don't want to ride after that, I'll go home. I've never gone home- it's always better once I get on the bike, even when it's cold and raining.