Which is harder: being a wife or a mother? Before you toss out that question at your next book club meeting, be sure to pour the wine, because the conversation is about to get heated.

And the answer is … well, in my experience, it depends.

Both marriage and motherhood are partnerships. I tried out the idea that my husband call me life partner instead of wife, providing weeks of amusement for my two sons, who now insist that I am their life parent. (Life mother, they tell me, is too gender-specific.) Silly as I think labels can be, the terms “wife” and “parent” aptly describe the two most important relationships in the business world: your business partner and your investor.

It took me a while to realize I have to work at my marriage every day. I believed there would automatically be a balance of power, sharing of tasks and whatnot. As I discovered, shortly after signing the marriage contract and certainly before unpacking the wedding presents, it’s not that rosy. Soon my life partner was commenting about my use of closet space: “Why on earth do you have so many shoes? What’s wrong with one pair in black?” There’s the TV remote, time spent with in-laws, and other let’s-not-go-there topics.

Eventually, my partnership did evolve to clarify our roles and the big vision of our lives. But if partners are not discussing issues, no matter how awkward, there are going to be bumps of the sort experienced by Robin Chase and Antje Danielson, the founders of Zipcar.

The two women met at daycare. (I’ve seen more companies founded through children’s activities than business clubs.) They came up with the idea of car sharing, but Robin had far bigger plans to grow the start-up. I have a nagging feeling Robin did not check with Antje to see if she was on board. You can guess what happened.

Robin, who essentially built the company, let the partnership drift as she knew confrontation would destroy the personal relationship. There go the families’ happy times together. I understand Robin’s reluctance to end her “marriage”; some parts were working, just not the business parts.

It was only when a second partnership formed — with a private equity investor — that Robin was pushed to act. Now I see the relationship between entrepreneur and investor as a parent/child relationship; power, at least in the beginning, rests with the investor. Zipcar’s older, wiser private equity investor encouraged Robin to cut Antje. I would have felt sick to my stomach to ask for a divorce, but it was necessary.

As a parent, I do not want to micromanage my child, but certainly offer guiding discipline. (“Please put down the Wii controller and pick up a book!”) In the same way, a good investor asks for tight management techniques and meetings with set milestones and goals. The big difference from real mums though, is that the investor will want the entrepreneur to grow up fast. The sooner the entrepreneur can develop, the sooner the investor can cut the apron strings, get back their investment, and exit.

As for Robin Chase, she survived her break-up, went on to win Business Week magazine’s top ten business designer awards, and sold out of Zipcar. I see that for her new enterprise, she’s not leaving her important relationships to chance. Robin’s new business partner is her husband (or life partner, as my two sons would say).

Jacoline Loewen is a wife, mother, and expert at raising capital as partner at Loewen & Partners.

For a podcast companion to this piece, listen to this months featured episode of the BusinessCast Podcast, "How to Find the Perfect Business Partner."