There's something about getting a wad of cash that threatens one's frugality.
The penny-pinching proclivity begins to waver in the face of potential purchasing possibilities. With all this money, I can actually buy stuff now! I can afford products and services that I couldn't enjoy before because of the lack of purchasing power that I now possess!
It is this same principle that has gotten many a credit holder carried away. Resist the temptation to spend hard-earned cash on nonsense. I suppose its because we spend the bulk of our early life not earning anything that the moment we do, we give ourselves the privilege to spend without consequence, and since we're all piggybacking off of our parents anyways, we are free to rack up debts without compromising our living situation.
Don't buy yourself into an unsavory statistical category and exercise a little restraint.
But everybody loves a payday, so why not celebrate?