"know your customer's requirement / concern properly ....... Before entering into a Contract!!!

An elderly man was having a calm walk when he happens to pass a brothel. 

One of the prostitutes calls out: "Hey Grandpa! Why don't you try?

The old man replies : " No I cannot ! " 

The prostitute : " Cheer up !! Let's try

The elderly man enters and performs like a 25 year old and then the prostitute says : "Oh Gosh ! And you still say you cannot"

The old man replies : "Aaah, sex I can, what I cannot is "pay" !!
.
Moral :
"know your customer's requirement / concern properly ....... Before entering into a Contract!!!