The first ice cream tastes great->highest return.
The second one ice cream tastes OK.
The third one ice cream tastes not so bad.
The fourth one ice cream tastes sick and makes you sick as well ->lowest return.
This is the law of diminishing returns as I read about sometime ago.The law of diminishing returns also holds good in case of pain as well.
The first sorrow makes you feel real bad. When you drenched off all your sorrow and cannot be morose further,it first becomes a "philosophical laugh" (like the Mera Naam Joker's laugh). Even then if you keep experiencing pain, you feel nothing at all.
In case of achievement, I am not sure whether the law of diminishing returns holds. One achievement brings more encouragement. But of course, you are more bound to commit mistakes. After Hitler's anschluss of Austria, he was encouraged and Czech acquisition became a matter of urgency to Hitler. He wanted to finish that one off.