Impermanence

Impermanence, also called Anicca or Anitya, is one of the essential doctrines and a part of three marks of existence in Buddhism. The doctrine asserts that all of conditioned existence, without exception, is "transient, evanescent, inconstant". All temporal things, whether material or mental, are compounded objects in a continuous change of condition, subject to decline and destruction. The concept of impermanence is also found in various schools of Hinduism and Jainism.

Anicca or impermanence is understood in Buddhism as the first of three marks of existence, the other two being dukkha (suffering, pain, unsatisfactoriness) and anatta (non-self, non-soul, no essence).

All physical and mental events, states Buddhism, come into being and dissolve. Human life embodies this flux in the aging process, the cycle of repeated birth and death (Samsara), nothing lasts, and everything decays. This is applicable to all beings and their environs, including beings who have reincarnated in deva (god) and naraka (hell) realms. This is in contrast to nirvana, the reality that is Nicca, or knows no change, decay or death.

Impermanence is intimately associated with the doctrine of anatta, according to which things have no essence, permanent self, or unchanging soul. The Buddha taught that because no physical or mental object is permanent, desires for or attachments to either causes suffering (dukkha). Understanding Anicca and Anatta are steps in the Buddhist’s spiritual progress toward enlightenment.

The Pali word anicca is a compound word consisting of "a" meaning non-, and "nicca" meaning "constant, continuous, permanent". While the word 'Nicca' refers to the concept of continuity and permanence, 'Anicca' refers to its exact opposite; the absence of permanence and continuity.

The term appears in the Rigveda, and is synonymous with Anitya (a + nitya). The term appears extensively in the Pali canon.

Impermanence and Attachment

As long as there is attachment to things that are
unstable, unreliable, changing and impermanent,
there will be suffering –
when they change, when they cease to be
what we want them to be.
(...)
If craving is the cause of suffering, then the cessation
of suffering will surely follow from 'the complete
fading away and ceasing of that very craving':
its abandoning, relinquishing, releasing, letting go.

...
Wikipedia