Loss of confidence

Here is a curly one, how come the moment I hear somebody say you can't do that (eg forge a visa) I think, lets give that a whirl - I wonder if I can talk my way through this one. Yet when I am wandering around alone I loose the confidence to try and convince the guys running the meat van taxi that yes my surfboard will fit. Why does surfing four foot alone seem so difficult, yet I blindly pull in to a six foot no way out sand spitting grinding barrel with a grin on my face ?