How do we know that prayer hasn't changed something in our lives?

This question was asked recently by another user and i missed my chance to answer it... Here's my reason: a href="http://i209.photobucket.com/albums/bb62/Randall_Fleck/Ineffective_prayerGIF.gif" rel="nofollow"http://i209.photobucket.com/albums/bb62/…/a ...what's yours?