Technical analysis is just one piece of information.
Example : If there is bad news about one company and their stock, but the public does not know it yet...then the prices may drop for no "known" reason.
If an earnings report is coming out soon...then bad people who know the bad news can illegally and immorally sell their stock and/or play the options market.
By watching the graphs, one might learn thru Technical analysis that something bad is happening. You may not yet know why or what. The news will pop up later, but then it might too late to get out.
That is why stop loss orders also can be useful. But they can also work against you or not work at all.
In October 1987, 1929, and at other times, one can watch the "Extraordinary Popular Delusions And The Madness Of Crowds..."
Getting out of the way of the crowds is a good idea and can be a profitable idea. This can also work when the prices are going up. Watch for "Tension on the Tape..."
The stock market no longer bets on whether a company will be successful or not. Today's investor bets on whether or not other people will be dumb enough to pay an even higher price later on.