I have a pet peeve. It is listening to non-technical managers, and sales people specifically in information technology speak about products they have never used.
At one point in my career I learned this valuable lesson. I was working for an online banking software company. We sold account aggregation software. This product gave you the ability to add accounts from different banks or credit cards and see them all aggregated on one website. I actually tried to avoid using the software myself. I thought I could learn the answers to questions from prospects and customers by studying the screen shots. I assumed I could anticipate what the questions would be on how someone would use the software in their lives. WRONG!
If you are selling a product, especially a product that is available for the general public, you must use your own product. I was promptly told by a more senior peer that if I didn't believe in the product no one will believe me when I tell them how useful it is. That was some valuable advice and it has proven to be 100% correct over and over again.
In my current position I have the opportunity to develop products for the masses. I still have project managers, and Senior Management always willing to give their two cents on how the new products should work. However, many times in these conversations it only becomes clear that they themselves have never used the current product, or any competitors product. The lack of understanding oozes from every suggestion that they make.
If I could always have one requirement on any project. It would be that everyone involved must use it! It makes a huge difference in the teams ability to speak the same language and understand the problems and goals.