Pain

Why do we feel it? Be it physical and emotional, was there a need for such a feeling? Was it a price to pay for other experiences like joy and love? Still, I wouldn't trade love for the exclusion of pain. I wouldn't trade joy for the exclusion of pain. Hmmm, can I trade jealousy for pain? Or anger? Or impatience? Why can't we trade a negative for another negative? Tsk