NEED to KNOW ... when do mere desires become needs?

The need to know one's self is a central concern in the pursuit of self actualization. At some point, this knowledge may be abandoned (I have heard), but it seems to be the indispensable scaffold. ("know thyself" was inscribed at the shrine of the Delphic oracle, very near the other critical injunction, "nothing in excess")

“ALL men by nature desire to know. An indication of this is the delight we take in our senses; for even apart from their usefulness they are loved for themselves ...” (opening line of Metaphysics by Aristotle, 350BCE). "Mandates" of sufficient urgency have come, over time, to be a constitutional element of the species, and we are guided by delight where deeper purposes may not be obvious.

WAYS of KNOWING must be in balanced lockstep:
“There are two modes of knowing, through argument and experience. Argument brings conclusions and compels us to concede them, but does not cause certainty nor remove the doubts in order that the mind may remain at rest in truth, unless this is provided by experience” (Roger Bacon, Opus Maius, 1268)