We made this grave mistake initially. For the entire first year, we were building products in isolation, without talking to real customers. We didn't have an operational business and made $0 in revenue, yet we were spending time & money on building products we assumed our potential customers would like. When we launched the products, we realised that our customers didn't need the features we had built. In fact, they didn't even need a product! For quick context - my startup, Flexiple, is a tech freelance marketplace. Our clients just wanted to work with quality freelancers and were happy to keep the logistics on email, phone etc. So, we ditched both the products and used Google sheets, email, docs etc. to run our business, and reached $100,000 in revenue! It was a costly mistake for us, since we lost $10,000 building the products initially and a year of precious time.