We all have a finite store of mental energy for exercising self-control. Some of us have less, some have more—but we all eventually run out of willpower steam. That’s why the more choices we need to make during the day, the harder each one is on our brain, and the more we start to look for shortcuts. (If you like, call this the "Oh, screw it" syndrome.) Then we get impulsive. Then we get reckless. Then we make decisions we know we should not make...but it's as if we just cannot seem to help ourselves.
In fact, we often cannot help ourselves: We have run out of the mental energy we need to make smart choices. That’s why the fewer choices you're forced to make, the smarter the choices you can make when you do need to make a decision. Say you want to drink more water and less soda. Easy: Keep three water bottles on your desk at all times. Then you won't need to go to the refrigerator and make a choice.
Alternatively, say you struggle to keep from constantly checking your email. Easy: Turn off all your alerts. Alternatively, shut down your email and open it only once an hour. Or take your mail program off your desktop and keep it on a laptop across the room. Make it hard to check—then you are more likely not to.
Say you want to make smarter financial choices. Keep your credit card in a drawer, and then you cannot make an impulse buy. Or require two signoffs for all purchases over a certain amount; then you will have to run those decisions by someone else (which probably means you’ll think twice about making the purchase and won’t even bother to ask).
Choices are the enemy of willpower. So are ease and convenience. Think of decisions that require willpower, and then take willpower out of the equation completely.