(Pāli; Sanskrit: anitya): All compounded phenomena (things and experiences) are inconstant, unsteady, and impermanent. (Practically) everything is made up of parts, and is dependent on the right conditions for its existence. Everything is in constant flux, and so conditions and the thing itself is constantly changing. Things are constantly coming into being, and ceasing to be. Nothing lasts.
The important point here is that phenomena arise and cease according to (complex) conditions and not according to our whims and fancy. While we have limited ability to effect change to our possessions and surroundings, experience tells us that our feeble attempts are no guarantee that the results of our efforts will be to our likings. More often than not, the results fall short of our expectations.
In Mahayana Buddhism, a caveat is added: one should indeed always meditate on the impermanence and changefulness of compounded structures and phenomena, but one must guard against extending this to the realm of Nirvana, where impermanence holds no sway and eternity alone obtains. To see Nirvana or the Buddha (in his ultimate Dharmakaya nature) as impermanent would be to indulge in "perverted Dharma" and would be seriously to go astray, according to the Buddha's final Mahayana doctrines. Other schools of Buddhism, however, feel uneasy with such a teaching.
