In his book Good To Great, Jim Collins covers the value of a "stop doing" list. His focus is on enduring organizational success, but the concept applies equally well for individuals. Our goal should be to decide yes or no, then either "just do it" as Nike recommends or "just say no". Real life is rarely that simple. Here are some of my key don't do items.
Don't assume against yourself. When you assume that something can't be done, it becomes a self fulfilling prophecy. I put this at the top of the list because it stops everything else. Henry Ford expressed it this way: Whether you think that you can, or that you can't, you are usually right.
Don't make big changes for small reasons. It is sometimes difficult to know whether a decision is big or small, but some decisions are obviously big. When your decision is big, the payoff should reflect it. Using liposuction to lose five pounds would be making a big change for a small reason. Using it to lose 105 pounds would still be a big change, but the reason behind it is big enough to consider.
Don't bet against the house if your goal is to win the bet. If the occasional lottery ticket is your idea of fun, go ahead. If it is your retirement plan, think again. Lottery tickets, roulette wheels, and other similar games assure the operator a profit. The more you play, the more you lose.
Don't over promise and under deliver. In Star Trek, Scotty consistently under promised and over delivered. In Star Trek Next Generation, Geordi LaForge delivered exactly what he promised, no more or less. Presumably, those who over promised and under delivered never got into, much less out of Star Fleet Academy. We can have an honest debate on whether under promising and over delivering erodes the trust of our colleagues. Over promising and under delivering is a formula for failure.
Don't spend what you don't have -- or what you do. There are cases where strategic borrowing makes sense, but they are rare enough that the act of borrowing should cause you to recheck your math. A store may sell you a TV for two years interest free, but make sure they don"t bundle in a loan insurance, an extended warranty, or some other gimmick to make money on something other than interest. Better yet, wait until you have money. Even then, shop intelligently. Warren Buffet owes a lot of his success to not buying things he could afford but didn't need.
Success is achieved by what you do, but your chance of doing the right things can be improved by identifying