2. People are absolutely key. Whether it's investing in an entrepreneur, taking money from an angel investor, or hiring a senior manager, A-caliber people are worth 10x those of B-caliber.
3. Cash is king. Lots of time is spent in business school looking at cash flow statements and analyses, but typically from a larger corporate perspective. But the one lesson that—one way or another—gets seared into the brain of every single entrepreneur is that the presence or absence of cash is completely deterministic for a business. Remember the Golden Rule of early stage finance: "the person with the gold makes the rules."
4. Keep everything in perspective. Bad stuff happens in every company, in every field, to every person. When one is young and starting out, it can seem like every setback is the end of the world. The more experience one has, the more one realizes that nothing is permanent except death. Perspective helps one 'do nuance', and makes it easier to not sweat the small stuff.
5. Technology is changing exponentially. This certainly wasn't taught when I was in business school, and it isn't taught in many places today. But it's the key tenet of Singularity University (where I founded the Finance, Entrepreneurship & Economics program) and it fundamentally affects every single business today that wants to have any hope of surviving, let alone thriving.
