1) You have to take rejection well
2) People don't see your product the way you do
3) Most people don't care about your product
5) Price doesn't matter
9 out of 10 times you're lucky if people don't slam the phone on you when you call them to introduce the product you are very passionate about. How come they don't care - well - that's life! Over time, you'll learn to deal with it!
We keep thinking about our product features as significantly different from others - but in the customer's frame of mind the cubic milli-meter you temporarily occupy in their brain is shared with several others!
Again we are always passionate about our product - but customers need a problem to be solved and are looking for an aspirin to solve their problems!
It is rare that the best product wins - functionality, technical chops etc. are often required but rarely the differentiating factor that wins you business. Customers care for a lot of things - but you must understand their view of the "best"!!!
As in everything we all do in life, rarely do we buy a product just because of price. Sure after choosing you, people do negotiate, but the final decision is rarely because of price in a non-commoditised sector.
Functionality, affordability, current value, option value, service and support, reliability, who we are dealing with are all factors with to pick a product.
I strongly encourage engineers to try this out - the best product suggestions I find come from engineers closest to (being) the customer!