BLSH - Buy Low Sell High

This is common wisdom to "buy low and sell high" when buying stocks. The author Doug Hall says this is a simple rule that's extremely hard to implement.

I use this expression and acronym not to perform the action but indirectly to remind me that simple ideas can be extremely hard to implement.

What rules do you know that fits this principle?

• Don't eat junk food
• Exercise at least 3 days per week
• Eat 5 servings of fruits and vegetables per day
• Don't watch TV
• Don't wait until the last minute