I'm not sure if a big wheel counts as a first bike but it is my first memory of riding a bike like object. My daycare provider had 2 or 3 of them for us to ride in her driveway while we were playing outside. I remember racing down the hill of her driveway and skidding to a stop at the end so we didn't land ourselves in the street. Inevitably someone would tip over and come inside with banged up and scraped up knees and elbows but somehow it never stopped us from doing the same thing the next day. :)
As far as a real bike is concerned...I vividly remember the first time I rode with my training wheels not quite level to the ground so my bike tipped side to side a bit while I was learning to balance. It was a scary feeling but once I got the hang of it and spent more time on two wheels it was very empowering!