Yoga Sūtra Chapter Two verse 5

अनित्याशुचिदुःखानात्मसु नित्यशुचिसुखात्मख्यातिरविद्या ॥५॥

anitya-aśuci-duḥkha-anātmasu nitya-śuci-sukha-ātma-khyātiḥ avidyā ||5||

Illusion is recognising what is transitory, impure, suffering
and other than essence, as eternal, pure, happiness and essence.

anitya - transitoryaśuci - impureduḥkha - suffering, pain, sorrowfulanātman - other than essencenitya - eternalśuci - puresukha - happiness; comfortable; pleasantnessātman - essence; the highest personal principle of lifekhyāti - recognitionavidyā - illusion

Commentaries and Reflections

T Krishnamacharya:

When something is understood differently from what it truly is, it is called Avidyā.
What is changing is taken to be non-changing. For example the mind.
What is subjected to decay is assumed to be pure, for example the body.
What is leading to suffering is taken to be the source of pleasure.
What is not conscious is assumed to be conscious.
All these errors in perceptions have many possibilities.
But the ultimate stage of Avidyã is to assume that we are the Masters, not Īśvara.

Paul Harvey:

“A necessary step in Yoga is to experience
a state of complete and utter disillusionment.
Arising from that is a state of Citta prepared
to give up its conviction of being the Cit.”

Avidyā is the illusion of recognising:
the ephemeral as the eternal,
the profane as the profound,
pain as pleasure and
the silhouette as the source.”

Patañjali reminds us of the pitfalls of the illusion (Avidyā)
of recognising (Khyāti) psyche (Anātma) as awareness (Ātma).”

“The Yoga Sūtra says you can’t change your life,
however you can change your perception of it.”

“The search for understanding is driven by misunderstanding,
though not always in the right direction.”