Seemingly sublime partnerships have been known, on occasion, to go the way of Martin & Lewis, Gilbert & Sullivan, Shaq & Kobe, and Caesar & Brutus. No matter how close the friendship, there's always the chance one or the other will take a knife in the back (or like Caesar, in the front). So how do you create a partnership that endures? You might think the answer is compromise. And you would be wrong. "We never, ever, compromise," says Penn Jillette, the taller, beefier, squawkier half of the comedy-magic duo Penn & Teller. The partners began performing together in 1975 and incorporated six years later. Their business now grosses between $10 million and $12 million annually. One of the rules they live by is that there is no holding back when it comes to arguing about what happens onstage. "Everything is set up as an intellectual argument where one brings up an idea and the other tries to shoot it down," Jillette says. "Either we find something we both like or we don't do it."

This setup might seem too charged for some, but honest collaboration is indeed the essential ingredient of a great partnership, according to David Gage, author of The Partnership Charter . Keep in mind that collaboration doesn't have anything to do with palling around at the poker tables. "You don't have to be great friends to be great partners," says Gage. In fact, "friends present problems because they may not know each other as well as they believe, or they might think it insulting to continually perform due diligence."

Maintaining a significant barrier between work and play keeps the focus on how to improve the company. Penn describes Teller as a good friend, but adds: "We perform at the Rio in Las Vegas 46 weeks a year, but we have dinner maybe three times a year. Our primary relationship is in service of the show." Focusing on the work is especially vital for the duo because they perform daring tricks like catching bullets in their teeth.

Another common mistake is to assume that as long as the business is doing swell, the partnership will be swell. Not so, unless partners share the same basic values. "Personal values form the underpinning of business decisions," says Gage, who advocates potential workmates take personality tests like Myers-Briggs or DiSC (Dominance, influence, Steadiness, and Conscientiousness) before entering into a partnership. He also encourages examining and drawing up guidelines for hypothetical situations that could later affect the business. Suggested topics: What if we have to bring on another partner? What if one of us gets divorced? What if a key employee is stealing from us? What if one of us wants out early? What if we go broke?

Back when they joined forces, Penn and Teller were too busy eating fire and palming cards to fill out a multiple-choice survey, but their enduring successful business proves Gage's thesis. "We show up on time, do our homework, and are supportive of each other," says Jillette. "But it helps that we are both libertarian, antidrug, teetotaling, skeptical, pro-science atheists."

Et tu, Teller? On second thought, no need to answer. A 30-year partnership says it all.