The main movie director loves their movie. Sometimes they love it so much they can be a bit of a bore when talking about it. Their obsession often gets in the way of people appreciating the movie at whatever level they choose. When an average cinema-goer, who enjoys a few hours of escapism, watches a trailer made by the main director with the precision and thoroughness which makes them a great director, featuring all their favourite scenes, they can be bored.
Some salespeople who consider themselves product knowledge experts do the same thing. They deep dive onto the how and what of their service or products without establishing a strong enough why. They sell so hard they buy it back, they give it all away and at the risk of introducing another metaphor, it’s as if the prospective client is thirsty and the sales person is a fire hose.