Krishna says (2.59) "sense objects fall away from the abstinent person, but not ras(longing) and longing ceases only when one realizes the supreme." Indriyas have a physical instrument and a controller. The mind is a combination of controllers of all sense organs. Krishna advises us to focus on the controller which sustains the longing.
Krishna uses the word 'ras' whose literal meaning is juice. When a ripened fruit is cut, 'ras' is not visible unless it is squeezed, same is the case with butter in milk. 'Ras' is the intrinsic longing that exists in indriyas.
At an ignorant level, Indriyas are attached to the sense objects and keep swinging between polarities of pain and pleasure. In the next stage, the sense objects.
like sweets fall away due to external circumstances like lack of money or doctor's advice but the longing for sweets remains. External circumstances may include morality, fear of God/law/reputation, ageing, conditioning etc. Krishna is indicating about the ultimate stage where longing itself goes.
Krishna gives a practical tip in Srimad Bhagavatam (11:20:21) where he compares Indriyas with wild horses which are brought under control by a trainer who runs along with them for some time. When he fully understands them, he starts riding them as per his wishes.
Two issues to be noted here are that the trainer can't control horses in one go as they will overpower him. Similarly, we can't just start controlling Indriyas, we need to go as per their tunes for some time till we understand them and slowly bring them under control. Secondly, we need to be in a state of constant awareness that we need to control Indriyas, even when under their influence.Awareness and longing can't simultaneously exist. Knowingly we can't be gripped by longing as it happens only in ignorance.
Source - Daily World