I have two degrees from Stanford University--a BS in Product Design, and a BA in Creative Writing. Stanford is renowned in both disciplines; the d.school is probably the world's leading center for design thinking, while the Stegner Fellowship for writers is one of the most prestigious in the literary world.
Yet the most important course I took at Stanford wasn't in either subject. Nor was it it the sciences or engineering. The most important course I took at Stanford was Peer Counseling.
The Bridge Peer Counseling Center is an all-student run counseling program that was started by the late, great Vince D'Andrea. While I was an undergrad, I took the Peer Counseling course, and later served as a TA for the program.
The heart of the peer counseling philosophy is non-judgmental active listening. This had a huge impact on me, since as an arrogant young prodigy (I started Stanford at 15, after skipping several grades and graduating as the valedictorian of my high school) my preferred mode of communication was the judgmental monologue (my family might argue that the monologue part hasn't changed much!).
Non-judgmental active listening means that you focus entirely on what the other person is saying, checking your understanding with occasional phrases like, "What I hear you saying is..." or "I think what you're saying is..."
Applied in a shallow way, it can seem mechanical and manipulative. But applied sincerely and skillfully, it is profoundly powerful.
The message it sends is that you're focused on the person, and are making every effort to understand them.
If you're a startup entrepreneur, you can apply this technique in many ways. Active listening helps you understand the real needs of your customers (rather than monologueing about the greatness of your product). It helps you relate to your employees and teammates (so you aren't blindsided by their actions). And it helps you hear what people are actually saying, rather than what you want to hear.