When it comes to combat, knowing what move an enemy is about to make and how long you’ve got to retaliate once it’s finished (if any) is paramount to not making mistakes. Bosses have the most obvious 'tells' (the 'Wind Up') and each 'tell' is specific to each move.
The wind up offers you your window of opportunity to pick the appropriate method of retaliation. Knowing when to block, roll (and in which direction), parry, backstep or guard break will very likely mean the difference between life and death (more so on the NG++ style difficulties where many enemies and bosses can 'one-shot' you i.e. kill you in a single hit).
Once you know how to prevent being hit; the next task is to get your own attack in there. So this is where the cool down comes into things. Most enemies stay still in a frozen state after attacking for a varying degree of time. This period of time is what we refer to as the 'cool down' period.
It may only last a second or two; but it’s your chance to make a sound judgement on how many hits you can get in before the enemy is ready to react. And it’s during the cool down period where most Soul players make the fatal error of getting greedy and trying to land one too many hits.
So each time you reach a new enemy it’s worth trying to bait them into doing an attack and then see if you can spot that move’s tell/wind up period and then how long you’ve got once they finish the attack (the cool down).