Dear friends, it is OVER. The first semester of business school was just as demanding and transformative as advertised, and now I'm damn ready for almost four weeks of vacation.

It's hard to believe that not too many years ago, I was a card-carrying socialist, convinced I was going to fight the good fight as a lawyer defending the powerless. I also despised the state of California in all its self-aggrandizing glory.

And now here I am, more than one-quarter of my way to a Berkeley MBA. (I realized that lawyers for the powerless were some of the least happy people I had ever met, and I also realized that the Bay Area is fun.)

So, I got these two big projects turned in two weeks ago, and four final exams out of the way. But it wasn't about the grades (which are sealed) or the homework. Rather, business school has been about changing the way we think.

I can't even describe the number school has done on my cognitive processes, not just in how I approach business problems, but how I approach life. For example, early on in Microeconomics we learned about "decision trees," a way of analyzing a series of decisions to determine their expected values, based on probabilities and payoffs.

A decision tree runs from left to right across the paper, like this…

The tree doesn't make the decision for you, however. You have to weigh your aversion to or "love" (that's the actual economic term) of risk. Decision trees do have one hard-and-fast rule, however: Always look right.

This is also known as "Don't cry over spilled milk," "It's all water under the bridge," "What's done is done," or simply, "Bygones." In other words, don't worry about sunk costs, which are to the left on the tree. Just do what makes most sense now.

In a personal financial example, consider this: You want a Saab really bad, so bad that you spend six years squirreling away every spare penny for it, because you don't want the bank to own a single rivet. One glorious day, you go to Sven's Motorworks and throw down $30,000 for the new car, and drive it off the lot with glee. Two days later, however, the car starts having problems, sputtering out at red lights. You bring it in to Gudmund at the local repair shop, and he says a pigeon had climbed into your engine at night and died, and all the feathers have been sucked into the intake system. This problem has in fact ruined the whole powertrain, and it's own a matter of days until the car just stops for good. The repair estimate: $15,000, and even then the car will never run the same.

But you see your neighbor is selling his only slightly-used Corolla for $10,000. So, what do you do?

The first thing you might be thinking about is the six years of vacations you didn't take so you could save enough for the Saab. But you shouldn't. The $30,000 is a sunk cost, gone forever. At this point, you have two decisions: $15,000 for a rebuilt Saab, or $10,000 for a used Corolla. And that's that.

It seems simple, but it also puts things into perspective. Suddenly, things that looked stupid started to make sense to me. My friend Mark dropped out of his PhD program after three years to take a job. My friend Ben dropped out of law school after one year to switch to business school. My friend Sheri left half a million bucks in stock options on the table at Qualcomm to go work elsewhere.

And when things collapsed a couple weeks ago with this crazy lawyer I was dating, suddenly the past between us (a few decent dates) didn't seem like a loss. The only thing to consider was the future (yes, she was crazy). The smart decision was made.

So, I learned: look right. I've been looking right so consistently, that I'm getting a crick in my neck, but it's the way to go.

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