By the time these "analysts" make their findings public, the brokers and investment houses they really represent have already bought that stock and driven the price up past the point of profitability for you. These banks and institutions have supercomputers connected by fiber to the stock market servers. Unless you're buying a stock they have no intention of buying that day, they're most likely pricing you out of that hot tip. Even if they weren't doing all of this, you have to compete against millions of other folks just like you reacting to this stock tip. Are you faster than all of them?
Are these analysts telling you at what point to lock in your gains and sell the stock? As Marty mentioned, they rarely do. Telling you when to buy, but not telling you when to sell is only half-good advice. The only time they tell you when to sell is when that company is nosediving and everyone is past the point of seeing any profit on those stocks. If that company is doomed, it's apparent to everyone and you didn't need an expert to speak on it. If it's a noticeable drop but they see it as temporary, they're telling you to sell while telling their hedge funds and friends to buy it up at a discount.
Picking when to buy and sell at the right moment requires a very high level of skill and luck. Imagine playing poker as a day job and the number of hands you'd have to win consistently for it to be profitable enough to live by. There are only a literal handful of people in a generation who can do this.