I've been witness to people who, even after suiting up, find an excuse to not exercise that day: all the treadmills are taken, their shoes feel funny that day, or they don't want to mess up their hair are just a few excuses I've heard. It's easy to talk yourself out of a workout, but that'll get you nowhere fast.
Instead, make sure you create manageable goals for yourself and a schedule you can stick to. On days you don't want to work out, fake it 'til you make it: you'll be surprised how easily it comes to you, but more importantly, how good you'll feel afterward. Exercise does boost endorphins, after all.