The quality of humility is so important in spiritual realization, that the failure to cultivate it will ensure the lack of success.

The living being in the embodied state has two coverings, the gross physical body, and a subtle body comprised of the mind, the intelligence, and the false ego (ahaṅkāra).  The false ego is the first and most powerful covering of the soul, which distorts the consciousness of the embodied being. The false ego will have you think and feel that you are all important, always right, and see everything with great clarity. Nothing could be further from the truth.

The false ego and the four human defects (to commit mistakes, be subject to illusion, a propensity to cheat, and greatly limited sense organs) make it difficult to perceive actual truth.  Humility counters these influences and makes us inclined towards submissively hearing from spiritual authorities and supports a way forward, towards spiritual enlightenment.