Is taking ‘Guru Diksha’ compulsory before choosing a Guru?

Sri Sri Ravi Shankar:

You don’t have to choose a Guru. The Guru Tattva is present in every good thing you learn in life, and wherever you learn it from.
Mother is your first Guru. As you grow older, there will be teachers who provide you education. Similarly, in each phase of life, the presence of a Guru will be there. The Guru Tattva is always present.
So whenever our mind feels that something would help us grow in life, it means that the Guru Tattva is present.