Substance of Bhakti is Surrender and Humility.
Surrender means to do anything at anytime without desire or expectation.
Patience is a symptom of surrender.
Surrendering our heart is surrendering our false ego.
Surrender sounds horrible to the one who wants to be a controller, but it is the sweetest and the most pleasing of all words for a devotee who has a humble heart.
If we take shelter of Krishna, nothing is impossible, everything is possible. As we are putting our hearts in the protection, under the influence of the Supreme Love of God.