Budgets are like diets. Both are tough to define. And neither one is easy to stick to -- especially when you're tempted over the holidays.

Experts say just like diets, budgets tend to be blown more often on the weekends than during the week. The theory: You've deprived yourself all week, so when the weekend hits, your will-power splits.

"It's easier to stick to a budget during the week than on the weekends," says certified financial planner Julie Murphy Casserly, founder of JMC Wealth Management in Chicago and author of The Emotion Behind Money: Building Wealth From the Inside Out.

Black Friday can certainly net shoppers some great holiday gift deals. But if you're not careful, experts say those "deals" could wind up costing you big in the long run by damaging your credit score.

Steve Schwartz, executive vice president of consumer services at Intersections, Inc., in Chantilly, Virginia, told WalletPop that it's easy to get caught up in the adrenaline-filled rush of Black Friday shopping. "But without a plan," Schwartz says, "consumers frequently end up with buyer's remorse." And a plunging credit score, too.