Some of the best decisions and designs at 37signals have emerged from intensely contested debates. Not just between Jason and me, but from anyone in the company. When sparks fly, some truly great ideas come to light.

The catch is that the heat must arise around the decision itself. Debates go off track when personal biases or old grudges come into play. So long as each party sticks to the merits, adding some fire will only unearth new angles and concerns.

This energy is so important to how 37signals operates that I consider it every time we make a hire. Is this person willing to fight for what they believe in? Will they stand up to me, Jason, or anyone else in the company if they think we’re wrong?

Detecting this rebel streak requires looking at a person’s full persona: online debates, choice of technology, writing or work samples, often just the ability to debate or question the interviewer in person.

Sometimes it’s easier just to detect a negative. Someone who’s unlikely to ever question you or your ways. A “yes man” who has only wonderfully great things to say about everything we’ve ever done. That’s a red flag.

Regardless of how you do it, find people with enough spark to care, fight, and campaign for what they believe in. What pushes you and makes you question your beliefs will make your company that much better.