It happens every time: Someone asks me for a favor, one that by every objective measure is all cost, no benefit.

But still: I don't have to "deliver" until three months from now. Plus, it doesn't sound like that much work. And who knows, it might even be fun. 

So I say yes. I'm in.

Until it's a week away. Then I start to kick myself. Until it's three days away. Then I start to dread it. Until it's the day before, when I would do anything to get out of it. 

"Why did I ever agree to this?" I think. "I have so many other things to do. What the (heck) was I thinking?"

Problem is, I wasn't thinking. Not really.

Instead, I fell prey to the inverse-square law of saying yes.

In science, an inverse-square law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity.

Think dilution: Spray paint on a surface two feet away, then spray a surface four feet away, and the coverage will only be 25 percent as heavy as it was at two feet. (Yay, math!)

The Inverse-Square Law of Saying Yes

The same thing happens with saying yes: The farther away the delivery of a request, the easier it is to downplay the eventual distraction. Or difficulty. Or time involved. 

Say a LinkedIn connection asks you to do a webinar for his company. It's easy to say yes if the webinar is next month. It's really, really easy to say yes if the webinar is in four months. 
And what if it's six months from now? Given that lead time, saying no almost seems rude. 

But it's not rude, especially since the most precious resource we have is time. 

As Warren Buffett says, "The difference between successful people and really successful people is that really successful people say no to almost everything." 

As Basecamp co-founder Jason Fried says, "If you like saying yes, get better at saying no. No gives you more opportunities to say yes to the things you really want to do/make/try/explore/discover."

Granted, we all like to think of ourselves as kind. As generous. And who are not only extremely busy, but extremely good at taking on even more.

But, as Bill Gates says, "It's not a proxy of your seriousness that you've filled every minute in your schedule."

Nor can you do everything, no matter how selfless the act or worthy the cause.

The next time someone asks you for a favor -- and by extension, the next time you consider adding anything to your schedule -- avoid the inverse-square law of saying yes by applying a different filter.

As Inc. colleague Jessica Stillman suggests, ask yourself a simple question: "If this were happening tomorrow, would I be psyched to do it?"

Answering that question will help ensure you add only the right things to your calendar: the ones that make the biggest difference for your employees, your business, and yourself.

And, in the meantime, you'll free up more of your time to think. To have great ideas. To strategize. To plan. To make smart, informed, thoughtful decisions.

Unless you would be eager to do it tomorrow, seriously consider giving long-range "opportunities" a pass. 

Because chances are when the actual day comes, you'll almost always wonder what the (heck) you were thinking when you said yes.