In The 22 Immutable Laws of Marketing I find law 11 the most interesting.
“The Law of Perspective”
It states that most of the time in marketing (and life) the long term effect of something is usually the opposite of the short term effect.
In the book Al Ries and Jack Trout use a ‘sale’ as an example. The short term effect of having a sale for your business is increased revenue. People see the lower prices and buy more. BUT in the long run your revenue actually decreases because your customers will wait for you to have a sale (and thus lower prices).
Do you know anyone that has been into a traditional clothing retailer that has purchased something that wasn’t on sale?
Eating poorly is another good example. In the short term you feel good, satisfied with your choice of junk food. Unfortunately in the long term the effects are the opposite!