Gambling is betting when the odds are against you.
When the odds are in your favor it is called taking a reasonable risk.
Good poker play is the latter.
For example, driving in a car is risky. There is the chance of death. However, the odds are greatly in your favor. It's highly unlikely that you will be killed in an auto accident (though some people will) if you drive safely. All bets are off however if you drive in a way that is not safe.
In the case of poker, there is a way to play that over time pretty much assures success. (I'm still trying to figure out what it is
) But the long-term success of good players shows it does exist. This type of play is
not gambling (which is why these players can have such confidence in it) though it does involve
risk taking. They know if they apply certain principles (which can be quite complex and multi-layered) winnings are "guaranteed" over the long-term.
That's the theory. In reality you have this thing call the human psyche which can fluctuate greatly in its ability to execute optimally. Even a good player can suffer a crisis in confidence. Bad luck, bad beats, lousy hole cards, yada, yada, can cause you to think there is something wrong with the way you are playing (and there may be) so you begin the tinker with your technique. The next thing you know you've lost your bearings and have succumbed to--you guessed it--
gambling, by reaching, pressing, and doing other things that are more expressions of your frustration and fear than the posititively expectant poker ability you've worked so hard to lay hold of.