Great question. It is not about you. Humbleness has nothing to do with acting humble. It is an experience of God. In that state of awe and wonder before the Creator and His Creation one feels how truly small one is in the entire scheme of the universe.
"Become the dust of the Saints; renounce your selfishness and conceit. Give up all your schemes and your clever mental tricks, and fall at the Feet of the Guru. He alone receives the Jewel, upon whose forehead such wondrous destiny is written." - ANG 45 Guru Arjan Dev Ji
This is the attitude that blossoms naturally when one understands that there are only two ways to live one's life: either through schemes and clever mental tricks designed to manipulate others in order to achieve your own goals and get what you want, OR to completely surrender to God and Guru and allow Him to deliver everything you need to you whilst your own actions are only to serve as His bhanda and do His will as He shows it to you. Serve everyone and let God serve you.
That is humility. It is not low self esteem. Low self esteem is when you occupy yourself with thoughts of your own guilt, inadequacy and unworthiness. Humility is when you understand that if Waheguru could have created anything better than you, He would have done. And then you give that back to Him in His service.