We don't lack it, it's just hidden inside us !
As other folks replied, we are used to a fast life style and that makes us impatient. However, that changes from time to time.
For example, I am least patient while waiting to submit my bills or waiting at the doctor's office but I am immensely patient when it comes to handling my child. Patience is something that I thought i lacked but now i know that it is something that we learn and build over a period of time..