The 10% Rule is one of the tools I have developed over the years as a guide to when to buy and sell shares. Given that my preference is to buy good shares when everybody else dislikes them, I used to have a tendency to jump into shares too soon, when they are still declining. As a result, I learned the hard way the truth of that old traders’ axiom “never catch a falling knife”. At other times, I have fallen in love with shares and watched them slide into nothingness while steadfastly ma ...