Hubspot's leaders were not heroes but rather a pack of sales and marketing charlatans who spun a good story about magical transformation technology and got rich by selling shares in a company that still has never turned a profit.

There are too many ways that a startup gig can go sideways. If the startup won't agree to hefty severance, pass.

A startup job is an investment, after all: Venture capitalists may wager money, but you're staking something more precious - your time. And unlike VCs, you can't spread your risk by betting on a bunch of companies at once. Start with TAM. That's 'total addressable market,' and if it's not big enough, there's no point in talking.

Most startups flame out or just muddle along. Your chances of spotting a unicorn, pre-horn, are incalculably small. But if, knowing that, you still want to toss aside your cushy job, at least listen to corporate vets who have made the transition.

Nvidia's CEO, Jen-Hsun Huang, is an engineer and a chip designer. He cofounded Nvidia and still runs it like a startup.

Nvidia's self-driving-car business grew out of a long-standing relationship with auto companies. Car guys used Nvidia chips for computer-aided design, then used Nvidia supercomputer chips to do crash simulations. When the car guys started thinking about autonomous vehicles, Nvidia leaped at the chance to help them solve the problem.

Conventional companies try to find new uses for capabilities they already have. Transformers look at what the market needs and then go build it, hiring new people and/or taking people off other jobs.

Why can't modern tech companies both grow and turn a profit at the same time?

Since 2011, Groupon has lost $730 million, and Zynga has lost just over $1 billion. Twitter has been in business for 10 years and went public in 2013. Since then, the company has lost $2 billion.

There was a time when a company could not sell its shares to the public unless its revenues were growing and it was turning a profit. Companies that lost money were deemed too risky for public investors.