The first day I ever rode clipless I did ok with my test ride on my neighborhood streets. The next day, after adjusting them too tightly (they were SPDs) I rode to a busy intersection and couldn't unclip. Luckily I was on an incline, so I managed to do an impromptu freewheel trackstand until I managed to get one foot free. After that I made checking the pedals part of my pre-ride routine, and haven't had any problems since.