[MrForbes]

First you have to get the bridge down. That is a significant challenge for many teams (it took us two days at the regional to get our bridge arm to work reliably). Getting on the bridge is easier if there aren't any balls in the way...which there are about half the time, it seems, since when you first lower the bridge the balls roll right in the way. Then you have to be able to drive the robot slowly enough and with enough control that it can balance. The kit drive train is a bit fast for doing this, and also most robots roll a bit after you let go of the joystick. This is assuming you were able to get on the bridge straight, and didn't fall off the side.

We found a whole bunch of ways to fail at getting on the bridge and balancing. Fortunately our shooting made up for it, but many (most) teams don't have that to fall back on.