Poker is a game that rewards the aggressive player much more that it rewards the defensive player. 

Aggression can cause players to fold better hands; it can cause people to lose control and call with weaker hands, and it can also lead to some amazing pieces of luck just when you need it. 

Being defensive means you are always going to traverse the tournament field with a fairly small stack, unless everything goes your way. 

A great example of the difference between an aggressive player and a defensive player is seen in the following example:

Defensive Player: The action checks around to the button and there is a raise. You are in the small blind with [As] [5s] and you decide to call. The flop is [Ts] [9s] [2d] and you check/call. The turn is the [6c], and you check/fold.

Aggressive Player: The action checks around to the button and there is a raise. You are in the small blind with [As] [5s] and you decide to three-bet and the button calls. The flop is [Ts] [9s] [2d] and you c-bet and he calls. 

The turn is the [6c], and you fire a second barrel and he calls. The river is the [Ks], making your flush, you move all-in and the button calls showing [Td] [9c] for a flopped two pair.

Can you see how the dynamics of the hand change once you start to apply pressure to your opponent? There are so many more ways to win a pot when you are aggressive.

Just make sure that it is controlled aggression and not mindless aggression. In the example given, you were chasing a flush draw and so this is controlled aggression.