Tuesday's guide discusses the though process behind aggressive players either raising or folding when it is their turn to act.
"The two main moves of the aggressive player are to raise or fold. Any other move and you are at the mercy of your opponent who has taken control. With control, your opponent has two ways to win the hand, whereas you have but one, to win with the best hand. Historically, the low limit games haven’t featured a lot of raising, especially pre-flop. You typically would find some limping in hands or one raise and some calls, but the prevalent aggression of higher limits has trickled down. Players at lower levels will often three bet (raise a bet/raise) to apply pressure."
The article can be found in the beginner guides sub section of poker guides area of the poker section in the sub tabs.