Volarecantare what you say works in an ideal world, but as we all know we do not live in one and what you will find is that emotions rule the market. Greed and fear go hand in hand. When you have no fear , greed will eventually take over and you will accept almost any level of risk. When the bubble bursts, fear takes over and everyone tries to sell at the same time.
Buffet says " When there is fear in the market, Buy. When there is greed, Sell!
Thats why he sold Pertochina at $21 and bought Goldman when he did....timing!!!