Imagine you were looking for Nirvana, Enlightenment, Liberation - whatever you want to call it. As a rational man you are, you would think logically:
Regardless of what Nirvana actually is (whatever it is), could it be that once I attain it, it would somehow end or expel me against my will? Could it be taken away from me? If it were that way, it would not be Nirvana. Therefore, Nirvana must be permanent.
Next, whatever Nirvana is, could it be that once I attain Nirvana I would still crave for something else or better than it? Could it be less than absolutely satisfactory? No, that would not be Nirvana. Therefore Nirvana must be absolutely 100% satisfactory.
Now, what does it mean for something to be permanent (to not be impermanent). Why are things impermanent? Things are impermanent because they depend on some causes and conditions for their existence. Once those causes and conditions disband, things fall apart and disappear. Therefore, all conditioned things are impermanent.
Next, what does it mean for something to be 100% satisfactory. It means when you have attained it you don't find it wrong or lacking or too much - even to the infinitely smallest degree. So any state of existence that has even the smallest amount of conflict between IS and SHOULD is not and cannot be Nirvana. Nirvana must be 100% without conflict, without craving for something else. When you have attained Nirvana (whatever it is), your IS does not have a SHOULD, it's perfect AS IS.
Now let's connect these two observations. Since conditioned things, things that depend on conditions, could be taken away from us (=could end), can they be 100% satisfactory? No, because they leave room for SHOULD, they leave room for wishing for more (wishing for the impermanence), because even as we have them we know very well that once they end that good possession or state of being or state of mind is now gone, is over. Therefore, all conditioned things are unsatisfactory.
Therefore, Nirvana must NOT be a conditioned thing. Nirvana must be 100% without craving for something else. Nirvana must be 100% conflictless AS-IS-ness, THUS-ness, SUCH-ness.
Having figured out that Nirvana must be unconditional, conflictless, without craving for something else -- even without knowing what Nirvana actually is -- you can keep on thinking.
If all conditioned things are impermanent and unsatisfactory, say I myself were conditioned on something external to myself, that would mean I myself would be impermanent. That would not be satisfactory, because how could I being impermanent attain something permanent such as Nirvana? That would not be possible. Therefore, the only way I can attain and stay in Nirvana if I myself were impermanent and unconditioned.
Now, let's examine this thing I call "I". Is my body permanent or impermanent, conditioned or unconditioned? My body is impermanent and conditioned. Are my feelings & emotions permanent or impermanent, conditioned or unconditioned? My feelings & emotions are impermanent and conditioned. Are my thoughts? My thoughts are impermanent and conditioned. Is my overall state of mind? It is impermanent and conditioned. Is my awareness? It is too impermanent and conditioned. Is there anything else I can point to and say "this is I"? How about this entire world, could I say I am this world? But this world, too, is impermanent and conditioned.
So if everything that I have or I am or I could be is impermanent and conditioned, and Nirvana is permanent and unconditioned, from that it would follow that Nirvana cannot be permanently and unconditionally attained by the I.
Wait a second! Could it be that Nirvana is attained without I, by dropping the I???
If Nirvana is unconditioned, conflictless, without craving, perpetual, JUST SO - could dropping the I be dropping the conditioned, dropping the conflicts, dropping the craving? When the I with its opinions and attachments is no more, could whatever remains be the craving-less JUST SO?
Could it be that Nirvana is attained by loosening one's hold, by letting go, by detachment, by not grasping, not insisting, not fighting for what is I/me/mine, what's deemed dear and right by the I?
Could it be that Nirvana is simply the unconditional peace of things as they are when the I stops creating the conflict?
But what does that mean, to stop creating the conflict, to stop craving, to stop grasping? How would it feel if it were so?
No internal conflict and no external conflict, what is that like? What is unconditional peace like?
To be at peace with things as they are, what is that like, in action?