How do I keep motivated when I'm overwhelmed with starting a business?

Each time I want to start a business, I feel excited in the beginning but when I think about sales, I feel overwhelmed and I bail out I'm a software engineer with full time job, I identify a business opportunity, I do all the planning, I create business model canvas / plan in few days, I do all the planning following lean approach , set a schedule etc. I know my ideal customer and market, briefly all the theory is done, but when it comes to taking actions, talking to people and get some clients on the phone, I feel overwhelmed, and afraid to get out of my comfort zone I end up dropping the ball quickly and the idea falls in the cracks.