Those Myers-Briggs tests that business schools love are notoriously flawed. In fact, several studies have shown that when people take the test a second time, as many as fifty percent of people will get classified as a different personality--even after only five weeks. By all means take the test, but take it about as seriously as your horoscope. I do not believe we're confined to these slots, although we may have predispositions.

I see personality evolution happen in the span of just a few months at Y Combinator. It takes work, primarily practice, to get up on stage in front of people and pitch. That's why YC insists that founders show up every Tuesday for dinner to pitch to their fellow founders. This has two effects: first, it helps people practice the important art of the demo, and in addition, it shames founders into having something new to show every week. If you see your fellow founders every day, it's hard to get a good answer to "What've you been working on?" because it's only been a day. If you haven't got a good answer after a week, something's wrong.

Start pitching. Pitch your cat for practice (they're notoriously hard to impress). The elevator pitch is standard for good reason--you'd better be able to explain your company in an engaging and understandable way within a few sentences--the time it takes to get in the elevator with that potentially life-changing person and successfully pitch her before she gets off at the executive floor.

If you want a stranger to give a damn about what you're working on, you'd better give a damn yourself. Speak sincerely, not like a salesman, and hack away at the words in your pitch until they are as few and as jargon-free as possible. Explain it to the executives like they're five. Well, a precocious five.

Excerpted from WITHOUT THEIR PERMISSION: How The 21st Century Will Be Made, Not Managed, by Alexis Ohanian. Copyright 2013. Reprinted by permission of the publisher, Business Plus. All rights reserved.