What's "Enough" Means...?

"Enough".. have you ever think those word means to? It's simple to said, but i think it's hard to explained. Actually "Enough" had lots of definitive, "Enough" for something that do you have. As Human has a different ways of demand to do something, to do have and to do want... Naturally when people gotta what they want, it's has a new motivated to get another one.  But Why does human never feels "enough"? I've try to define those word from my views it's adjustability with demands and abilities.