TA are basically crap. You can't reliably predict future looking only at the past market behaviour. If it worked, we would all be filthy rich.
'Charts' don't behave, they reflect the past and nothing more.
It usually goes like this: some guy makes TA prediction, if he hits - he looks like a knowledgeable expert, if he misses - he says "Ooops, I've misread the chart"; "Turns out it's not 'head and shoulders' it's 'cup and handle'!" or similar bullshit.
That being said, there's also the concept of "self-fulfilling prophecy". If enough people believe in TA and they accept the same patterns, then they could have enough power to influence the market and actually force it to follow the TA. Simply, if suddenly everyone starts to believe that certain stock will crash (even if the belief is baseless) - then the stock will go down, because no one buys and everyone dumps.