Marginal Benefit

Did you really need that fourth slice of cake? Like...the first one was delish. You hadn't really eaten all day, so yeah, it's understandable that you had room for the second and, well, you kinda wanted it.

But three and four? Really low marginal benefit to your sweet tooth, which was already on diabetic overload.

The benefit of that first piece? Huge. You needed the sweet. (And you deserved it, right? You went all day with zero traffic tickets.) So its marginal benefit was high, in that it sated that desire. The second piece? Well, had you gone without it, life on the planet for you would not have ended. It had some benefit. But less. And then three and four? Horrible. Negative marginal benefit, actually. Now you feel full and bloated and you regret them ruefully, as you slip on ever-tightening pants in the morning.