How do you overcome insecurites?

Insecurities. You already started the process. You acknowledge its existence. Cognitive therapy is a well-established form of treatment that can help you with this condition. I prefer the term eclectic therapy as it encompasses all kinds of interventions.
Fake it. What worked for me -- find a few friends who are wiser, kinder, and braver than you and who really care about you. Then step as boldly as you can into the situation that frightens you, with their guidance and unconditional support. Not to do this, big bruce, will be to doom yourself to a worse and worse life. The best cure for fear of heights is to take up skydiving. Be a hero, big man!