Knowing your product too well is not necessarily an asset when it comes to marketing, especially if you created it yourself. There is often a tendency to overvalue features which were difficult to code rather than features which add real value. Knowing your consumers is far more important.

You don't need "a lot of time explaining it to him in full details" - he doesn't need to know all the details. If you can't explain the product to him in under a minute, you need spend more time thinking about what is important and what not.