How would you know whether a financial market was in a "boom" (as opposed to just a nice "rising market")? Apply your indicator to the US stock market from 2010? When should I have exited? If I had done that, how much money would I have given up (if I was investing, say, a $100,000 portfolio). 

Remember, if you say, with hindsight, that I should never have exited, give me one good reason to trust your indicator today? What are the main reasons financial markets have gone through boom and bust cycles throughout history?