Mentally, I try to bail before every single encounter I'm scheduled to have. It could be having coffee with a friend that I haven't seen in awhile, or it's putting on a presentation in front of a room full of people.
People assume that because I do improv or preach about taking risks, that I don't have these feelings. But, I do. Every single time.
When I tell others about my dread, they are surprised. They see me get up, take my turn to speak and, in their assessment, I do it well and without abashment. Truth be told, I am surprised every time I feel dread, too. Part of me is embarrassed that it still happens, but another part of me knows that it means that I'm human. Once the speaking gig begins, or the other person sits down across from me at lunch, the dread leaves immediately.
By the end, I'm always glad I didn't give in to the dread and abandon taking my turn to speak.
If I let my natural feelings win, I would play it safe 100% of the time.
The next time you think about bailing on something because you're nervous or worried it won't turn out right, do what I do; tell yourself to start walking. Place one foot on the ground and then surprise yourself when you arrive wherever it is you need to be.
Then, repeat that over and over.