Michael Corleone, in the third part of the American epic “The Godfather,” says it best – “Friendship and money: Oil and water.”

Corleone, who had learned a thing or two from his dad about money and friends, not to mention money and family, was speaking to the Archbishop. The corrupt clergyman, now wearing a new hat as head of the Vatican Bank, was trying to drum up some business with his old friend from New York. But the newly minted Don was not about to mix money with friendship.

If only the rest of us had learned this from our own fathers! From trying to get other parents to buy our kids’ Girl Scout cookies to Martha Stewart’s dangerous liaison with Samuel Waskal we should know what tangled webs we humans can weave.

It always starts out with the best of intentions. Sam simply wanted to share his big idea and the wealth to come of it with his close friend Martha. What happened when it appeared that the wealth was a vision rather than reality, well, that remains a bit unclear. But Martha is certainly not alone in being the recipient of a good tip gone bad.

Sharing information with a friend is bad enough – even when it doesn’t qualify as illegal. Hiring a friend can be a nightmare.

Back in the 1990s, I ran a small financial magazine for a major publishing company, which was doing quite nicely in a comfortable niche of the market. Cost controls were not what they were to become a few years later. I had a bunch of friends who were freelance writers. So I hired a couple of them to work for the magazine. Why not?

At first, it was kismet. Each day was a party with a purpose – to get out a magazine. We would chat a bit and get to work. I felt that I was doing good while getting a good job done – my friends were well qualified and I was giving them work that they needed. What fun!

It did not take long for things to deteriorate. The first hint that kismet had a dark side came as I rushed out of my office one morning to get to a meeting. I glanced over at my friend Nancy (names have been changed to protect what shred of friendship is left) and noticed that she was reading a book at her desk. Poetry! As our eyes met, she lowered the slim volume onto her lap, then slid it further from view.

Okay, fine, I reasoned, some people make short personal calls; others get spiritual refreshment from Sylvia Plath.

But, of course, our internal dialogues, fueled by all that we knew about each other – all past injustices and favors – had begun. For my part, I felt betrayed. I brooded, “How ungrateful. I helped her out when she needed work! Next thing, she’ll be filing her nails at the desk.” For her part, it went something like, “What a witch! I’m doing the work – I can’t take time to glance at my watch?”

Now this was unfair, mostly on my part. Instead of talking with her in a straightforward fashion – a businesslike fashion – I accumulated the infractions. 1. Reading at the desk. 2. Late with copy. 3. Bad copy! 4. No copy! 5. Sick day? My internal conversation with myself had degenerated to the point where I was so annoyed that I couldn’t even look in my friend’s direction to see what poetry she might be reading.

Pretty soon, she quit.

It’s all about boundaries, a word used historically to delineate where property began and ended. Today it is used clinically to describe interpersonal and family relationships. According to Freda Walsh, an expert on family therapy, boundaries are “the rules determining who does what, where and when.” Boundaries, she writes, “must be clear and firm yet permeable.”

Unhealthy relationships flourish when boundaries are unclear. In my case, the confusion grew over what I was supposed to feel as a friend as opposed to what I was obligated to do as a boss. The history my friend and I had between us served as a catalyst to a turn a healthy relationship into one that was neither businesslike nor friendly. Like most relationships in which the boundaries have been breached, this one ended abruptly.

It could have been worse, I suppose. In “The Godfather” breached boundaries often led to bloodshed.

Ms. Bailey is a writer and therapist in New York. She can be reached at ebailey@nysun.com.