Pleasure and pain

Any living creature has tbe followint feelings in common.
They are
1)Hunger
2)fear
3) Urge for reproduction.
In additin to the above humans have the added advantage of expressing ing pleasure and pain.
When a human feels the pleasure he expresses it in many ways.
So also he expresses the feeling of pain in many ways.
The only difference is that at the time of feeling pain the human forgets that the same senses which carried the sense of pleasure are now carrying the feeling of pain.
Why is it so?