To put it in perspective, think about how excited you would you be if your boss raised you salary by $100/week. You would probably do cart-wheels down the hall. Now think if you went out for dinner and drinks with friends to celebrate, that same $100.00 could disappear in a matter of hours.
We need to looked at our expenses like we look at our income. If your boss shorted you an hour on your paycheck, you would probably march into his office and demand that it was fixed. Now how you would react if on the way home you noticed the grocery store accidentally charged you twice for a 24 pack of toilet paper. You may go back in and tell them, but then again it might just be more effort than it is worth.
Just remember whether your earning or spending, money-is-money-is-money. Finding a $5 bill on the on the ground, should be just as exciting as using a coupon.