Conventional wisdom: All you need is love!
On the contrary: The wrong spouse can kill your chance at success. Choose whom you marry very, very carefully.
Want to doom your chance at business success right off the bat? Marry* the wrong person. When I see a room full of twenty-something would-be entrepreneurs, I know the biggest decision (and possibly biggest mistake) of their lives will be made within the next five years--and no, it's not going into business for themselves; it's choosing whom to marry.
Most of them will devote less time to thinking about the impact of that decision than about their plans to start a business. Commit yourself to the wrong person and you make it 10 times harder to succeed.
Marriage is about being in sync. If the person you marry isn't a risk taker and you are, or if he or she spends money like there's no tomorrow and you're more conservative, you're going to end up putting your energy into fighting about your startup instead of getting it off the ground.
Don't leave it to luck.
I was lucky. I married someone who bought into my business plan. When I came home from my job in insurance and told my wife I couldn't work another day for a bunch of people who weren't listening to me, she said (in so many words), "Let's sell the house and start a company." It was just about that simple.
It has to be like that. Everything else about business is complicated and time-consuming, so you need someone at home who's fully in your corner. Of course, when we got married, we weren't planning to start a business. But we were on the same page about money and risk and committed to each other's dreams. And that has made all the difference.
My wife and I both made sacrifices and we both took time to focus on our professional growth. I supported her when she went back to law school. She worked as a lawyer so I could focus on growing the business without the pressure of making enough income to support the family. She left a job she liked when I needed her skills at the company. We both saved money all our lives, and shared a common goal: not making money, but growing a business we could be proud of.
Moreover, we not only had common goals and aspirations, but we also were committed to the realization of one another's dreams. And that has made all the difference.
The other kind of rebound.
Want to really, really doom your business? Get divorced. I can name half a dozen businesses that have gone belly up after protracted legal battles over the dissolution of marriages that no amount of couples counseling could ever have saved. The "sturm und drang" of deciding how to divvy up just the assets and visitation with the kids can turn your attention and energy far away from even the day-to-day operation of your business.
Even if your business survives, you'll likely wind up financially with a lot less than you anticipated--and, of course, you're never protected from the emotional fallout of a divorce. The more successful you are and the longer you've been together, the more you've got to lose. You lose your partner, you end up in the hole, and you're stuck rebuilding capital and catching up. It leaves a scar.
Your spouse may not run your company with you, but he or she is still your business partner in a very real way. Starting a company is hard enough--don't set yourself up for failure with an unsupportive partner. Sure, marry for love, but don't be an idiot about it: Marry for business savvy, too.
*Take "marry" as a shorthand for any significant life-long commitment.