How to get customer before building? I will not promote.

Lots of mixed confusing advice out there. Build, they will come, get customer first and then build, just build MVP, just MVP is not enough, or just become a copy cat cuz you just want a small company and not 1B company, etc. In my experience, selling is hardest. You become just another spammer in the emails, LinkedIn, phone, when you reach out to people. So how did you find your idea and validated it? I have experience in few industries, but I always had hard time coming up with good ideas and selling. How to do it right way? I have been lost in this maze for last few years.