There's an element of gambling to all investing....I think of it terms of black jack, you get dealt two 10s, and the dealer is showing a 6.  Conventional wisdom says to split the 10s at this point because the chances of the dealer busting are high....but nothing is assured.  Any one who's played blackjack has likely experienced splitting those 10s only to see the dealer turn over a 5 and then get dealt a face card.  

Of course you can count cards, but even still that is simply to improve your odds....to know when to increase your bets when the numbers are in your favour.  I view TA as being a little bit like counting cards....