I’m a firm believer in say-what-you’ll-do, do-what-you-say. If I make a promise, I try hard to keep it. If I don’t think I can do something, I don’t commit (most of the time–I’m human, after all). I figured this was pretty standard procedure for everyone, but an event that occurred several years ago set me straight.

Someone close to me and I were discussing our busy schedules, and after hearing about all the projects he had on his plate, I was convinced that he had way overcommitted. I encouraged him to reevaluate and extricate himself from a couple of things, hoping to avoid frustration down the road. He was adamant that he would stick to his guns, even though he acknowledged he couldn’t get it all done. Here’s what he told me:

If I can only complete 80% of what I’ve promised, then I’ll promise 120% of what I think I can do. That way, I’ll get 100% done.

Stunned silence followed.

Any way you figure that, it just doesn’t work. What about the people who were promised something who didn’t receive it? Just because they fall outside the so-called 100% threshold, that doesn’t mean they’ll be any less disappointed. I’m sorry, [friend, boss, child, colleague, teacher], I didn’t do what I said I would, but look at all this other stuff I got done. Aren’t you proud of me? Yeah, right.

Besides that, the math doesn’t work: 80% of 120% is 96%–not 100%. No matter what, someone is going to end up frustrated and disappointed. The damage to your credibility isn’t worth it; sometimes you just have to say no. Otherwise, all you’ve got is fuzzy math.