At the very beginning of the Gita (2:14), Krishna says that the meeting of the indriyas (senses) with the external objects causes polarities of pleasure and pain. He tells Arjun to learn to tolerate them, as they are transient. In the contemporary world this is expressed as, 'This too shall pass'. If this is inculcated at experiential level, we can transcend these polarities to find them equally acceptable.
There are five indriyas viz. vision, hearing, smell, taste and touch. Their corresponding physical parts are eyes, ears, nose, tongue and skin. The sensory parts are those parts of the brain which process the physical inputs of the respective organs.
However, these sense instruments have a lot of limitations. For example, the eye - it can only process a particular frequency of light which we call visible light. Secondly, it cannot process more than 15 images per second and this is the basis for the creation of videos and movies giving us the pleasure of screen watching. Thirdly, it requires a minimum amount of light to be able to view an object. These limitations of indriyas , hinder our ability to differentiate between the Sat (permanant) and the Asat(impermanent) and make us perceive the rope as a coiled snake.
Even the sensory parts of these instruments in the brain are handicapped by the limitations of the instruments. Secondly, they suffer from the fine-tuning done to them especially during childhood, which is termed as hard wiring. This results in motivated perception, to see what we want to see.
This inability to see Sat and the tendency to gravitate towards Asat results in misery. Krishna says (2:15) that when we maintain a balance during the onslaught of the polarities of pleasure and pain, we are eligible for the Amrut( moksha ), which is liberation here and now.
Source - Daily World