If you're doing a favor, the answer to the question is pretty darn obvious. You're giving your money, time or energy to someone else, which means you'll have less for yourself.
But what about when a friend suggests doing a favor for you? In that blazing moment of joy that comes when another human being offers you free help, you still need to pause and consider. Because even if that person wants to mow your 10-acre lawn for free (clearly, a dream sequence), you will have to give up something. It might be control: Maybe the person chops off the grass at 3 inches high when you prefer 2 inches, or uses pesticides you don't like. It might be freedom, like the person needing you to be home on Saturdays to let him into the garage. In my example, of course, no matter what the cost is, your answer is yes, followed by multiple slobbering thank-yous. In others, little issues like freedom and control may be big fat deal breakers.
2. Does this option have an expiration date?
All too often, I feel like I have to provide an answer right away, because if I don't get that "Yes!!!!" in immediately, the job offer will be given to somebody else, or the opportunity—to say, get a free haircut—will shrivel up and disappear...forever. A more honest way to phrase this is that fear is running the show, and nobody makes the right decision based on that emotion.
As with almost every single thing on earth—save for candy apples at state fairs, which you need to agree to immediately as a matter of principle—waiting can radically improve the calmness and quality of your reply. Furthermore, most opportunities do have a shelf life that's longer than you think, allowing you to weigh your options, get advice, listen to your intuition and lie there in bed at night arguing with yourself until one side wins—insuring that your "Yes!!!!" the next morning comes with genuine exclamation points.
3. What's the big risk, and what's the tiny risk?
You want to leave your job and start your own company. The big risk is what happens if you don't make enough income, lose your house and have to move in with your parents in Toledo. The big risk will appear as a woman in hot pants screaming through your brain with her hair on fire. What she is doing is distracting you from the tiny risk, the one you haven't thought about yet. For example, what if you do start your company, and you make enough money, but you have to work 22 hours a day and never get to go out on a date until you retire at age 83?
4. What do you really want?
Some of us occasionally say yes to one thing because we really think it might lead to another thing. Let's pretend you have a friend named Greta, who lives in Germany. She's got a wonderful 17-year-old daughter, who needs a place to stay in America for the year, and you agree to it. You tell yourself that you're interested in cultural exchange and that you adore young people. But in some dark, less-generous corner of your mind, you're thinking, "If I do this, maybe Greta will let me stay in her house in Berlin next summer." Should you force yourself to look at that bit of thinking, you might just want to change your response to "Okay, Greta, I'll house your only daughter, but I'd like to cut a deal with you about next summer." Which may be a little more direct than you usually play things. But it just might also save your relationship with her, if not improve it. Everybody loves honesty, even people with homes in major European capitals.
Next: The other motivation you need to consider