When my son was little I created an Ego Wall for him. I started by hanging his karate belts with Cub Scout pins on them. Every award and certificate he earned over the years was added to that wall. It became an everyday reminder of how great he was.
We all should have an Ego Wall. (You can call it something else if you want.)
Hang your diplomas, certificates, awards, Toastmasters ribbons – whatever represents success for you.
When you are feeling less than confident, go look at the wall. Before you give a presentation, go look at the wall. Have the wall in your line of vision when you are working with clients or making important calls.
It will remind you how wonderfully capable you really are.