How do you decide when to use emotions and when to use logic to deal with everyday situations? originally appeared on Quora - the knowledge sharing network where compelling questions are answered by people with unique insights.

Logic and emotion are not mutually exclusive and shouldn't be. They work best when used together.

When I was a graduate student at Stanford, I had a classmate -- nice guy, bit intense -- who designed an Excel model about how to have a family.

It was the epitome of logical thinking. I'll walk you through what I remember:

To make an Excel model, you need:

a) Inputs
b) Equations
c) Outputs
d) Measurement

Inputs: He diligently asked questions and researched facts related to his model: costs, health, time, etc. He considered how much should be saved for retirement, how much daycare costs, how much time together successful marriages require (he wasn't married). And many, many more. I think he used curves for most things.

Equations: He then answered 'How do these variables relate to one another?' Directly, incrementally, exponentially, not at all? And he put it all into the model.

Outputs: His model predicted results and trade-offs. For example, if you have a child in your 20s you will be earning less and saving less, and it might affect your career, your retirement, and what you can provide. If you wait until your 30s, you'll be financially stable, however, professionally unable to take time off to have kids. (As far as I know he didn't consider male/female division of labor.)

And finally, having done all these things, he had a set of answers, which he needed to interpret in order to drive decisions, thus;

Measurement: What was the value placed on each outcome, and how did they compare? This is where logic falls short and emotions -- natural reactions to instincts and preconceived beliefs -- are needed.

This guy was an extremely smart and sophisticated, but I don't think he understood the limitations of his logical method. I think he believed this model would tell him what to do.

It didn't. Couldn't.

Unless you have measurement and a value system, you can't make decisions between two very similar things. You know what will happen in each scenario, but not which to choose.

Is logic going to tell you if you care more about putting your kid into day care vs. getting a nanny? Sure, you know about costs, time spent with each kid, socialization benefits, etc., but if you keep asking, 'Why does that matter, why, why?' you'll be stuck and then it's emotions that help, not logic.

Emotions and logic shouldn't be mutually exclusive; humans need both to make difficult, important decisions.

Emotions aren't just "I feel mad, grrrr!". They're the manifestation of a tension within ourselves, or the lack thereof. Whether it's a value being ignored, or a preference being honored, emotions remind us what really matters.

I had always relied on my emotions because logical equations didn't make sense. If I felt angry, I knew something was making me feel insecure or threatened, and I'd figure out what. But at logic, especially if it involved numbers, I was helpless.

Except living on emotions isn't good. I never felt grounded, or very smart. So I spent the last 10 years of my life getting better at logic. I went to business school. I worked at McKinsey.

I'm balanced now, but emotions are still my primary language, so to speak.

My guess is that you -- like me, like most people -- are naturally better at one or another. If I've learned anything, it's that you need both working together.

Don't separate emotions and logic or assign them to different academic or life realms. Embrace both and balance them in everything you do.

If I have to make a decision, I'll use logical reasoning because it's not natural for me, and I'll push it as far as I can. If I get to an obvious tradeoff-Option A leads to death, Option B doesn't-great, decision made.

If not, and if I still cannot make a decision, then I gut check. How do I feel about this? Angry? Why? Happiness-why? What are my deep truths that cause these emotions?

Perhaps what I'm saying is treat your emotions logically, and your logic emotionally, and you'll develop really amazing cognitive, judgmental, and philosophical capabilities.

Yes, I gut-checked it. That sounds right.

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