There are various ways in which the truth of the universality of impermanence is spoken of. Figuratively, the action of time is compared to the wheel of a moving chariot (which only touches the ground at one point at a time), an ever-flowing mountain stream, a bubble, a mirage, the sound of a bell. Analytically, ‘impermanence’, is to be observed in the fact that all things exist in dependence on something else, arise out of and become something else: no thing exists in isolation, no thing possesses stability. It is precisely in this respect that nirvāna is to be understood as the direct antithesis of anicca, that is, as comprising duration, stability, and permanence, and why it is regarded as worthy of our aspiration, unlike the things of this world. The teaching on anicca links up with the Buddhist doctrine of ‘dependent origination’ (paticca-samuppāda) which states that ‘all things have a beginning’ and that ‘all things with a beginning must have an end’; the doctrine of anicca draws attention to the fact of their demise. The paramount importance of anicca in Buddhist teaching is spotlighted in the Buddha's last words, ‘decay is inherent in all things’.
In consequence of all this, Buddhism teaches the practice of aniccānupassanā (‘contemplation of impermanence’; cf. VIPASSANĀ) as the way of realizing the truth of impermanence. The actual process of contemplation involves ‘watching’ the rise or appearance of a given datum, verifying its ‘dependent’ or ‘caused’ origin; then, by the same token, ‘watching’ its subsidence or disappearance and verifying its transient characteristic.
Acceding intellectually to the truth of impermanence is termed in Buddhism the acquisition of ‘right view’ (sammā-diṭṭhi; see AṢṬANGIKA-MĀRGA) and is synonymous with entry on to the path to enlightenment.
"Anicca." The Concise Oxford Dictionary of World Religions. . Encyclopedia.com. (October 20, 2018). http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/anicca
"Anicca." The Concise Oxford Dictionary of World Religions. . Retrieved October 20, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/anicca