I started my first two companies when I was 19. Both companies were disruptive, so there weren't many people (friends and family included) who understood what I was doing.
1. Start with a belief in yourself and your end goals.
2. Don't substitute anyone else's discernment for your own.
3. Limit mistakes by understanding what you know and What You Don't and seek qualified advice for what you don't know. Many engineers know nothing about selling, so identify a pro and put them to work before the product is viable.
4. Strategies that defines A. who your core customers are, B. where they are, C. how to reach them and D. the best way to communicate your product's value proposition are fundamental keys to a return on your investment and significantly mitigating disappointment.
I wish you the best and hear your frustration. Understand that being concise in your product launch limits errors and that is the relief you are seeking. Cheers!