In the whole creation, the origin is never seen. A seed is sprouts, but what is happening inside the seed is not known. Similarly a baby is getting formed in the womb, but it is not visible outside. A river is born somewhere, but you can never really go to the source of the river. So the origin remains a secret.
Similarly, death is also a secret. Your origin is a secret and what happens after death is also a secret. From the subtle to the gross to the subtle again. And from the subtle how again it comes to the gross is again another secret.
So when you look at the secret, there is amazement and amusement in the mind. A 'wow'. This amusement is the basis for yoga. When you are amused by the creation, that means the preface of yoga has started.
Children are amazed by everything. They look at their fingers with amazement. They look at flowers and butterflies with amazement. They look at the stars in amusement. So, when amazement or amusement dawns in life, then yoga (synonymous of union) has also started.