What you write here is very true. Sometime, actually, probably quite often, motivation doesn't occur until you've started the activity you were seeking motivation for in the first place.
I think wanting to get fitter is a classic example. I know I've been guilty of this in the past. I wait until I feel like I'm motivated to start exercising, but in reality, that time is never really going to come. But, if I start exercising, no matter how I feel, motivation comes as I start to make progress - I can run further, faster, than the day before which builds motivation to keep pushing forward; some of my clothes start to fit better, which produces motivation to keep exercising so that even more clothes will fit even better. This has only occurred because I started, not because I waited for the perfect time.
Thanks for writing this - it's a good reminder to just get up and get on with it rather than waiting for all of the stars to align perfectly.