We do not ‘defend’; we educate. Never ‘what do you think,’ but rather ‘does this accomplish the goals & meet the needs of your users.’ The words we use to describe the work are just as important as the work itself. If you can’t explain it, you’re not done designing it yet.
Get over this fear by using the 70% rule from the Marine Corps. As long as you have 70% of the information to make a decision, 70% of the resources to complete the project, and you’re 70% sure you’ll succeed, then you’re ready to go. The heart behind the 70% rule is that it’s impossible to be fully prepared for anything. Trust your gut and get started.