मात्रास्पर्शास्तु कौन्तेय शीतोष्णसुखदुःखदाः।आगमापायिनोऽनित्यास्तांस्तितिक्षस्व भारत॥
mātrā-sparśās tu kaunteya śītoṣṇa-sukha-duḥkha-dāḥāgamāpāyino ’nityās tans-titikṣasva bhārata
Word by word
The verse says
Contact with the world brings cold and heat, pleasure and pain. They arrive and they leave. They do not last. Bear them, Arjuna.
In plain words
A shift from the eternal to the ordinary.
Cold and heat. Pleasure and pain. Krishna puts them in the same list on purpose - the same kind of thing, happening to you from outside.
And the key word: they come and go. That is their nature. Not a problem with your life. The way contact works.
Where you've felt this · in health
You are standing in a cold queue at the post office. You do not decide that your life has gone wrong, or that the cold will never end, or that you must solve it right now. You stand there and it passes. That ordinary skill is what is being asked for here, applied to much bigger things.
Going deeper
Titikṣasva - bear it, endure it. The word matters, because it is easy to hear this verse as do not feel anything, and that is not what it says.
Endurance assumes sensation. You cannot bear what you do not feel. Krishna is not asking Arjuna to go numb; he is asking him not to treat each arriving sensation as a verdict on his life.
The technical term is mātrā-sparśa - the touch of the measurable. Contact between a sense and an object. Cold is not in you; it is what happens where skin meets air. The same is true, Krishna is suggesting, of a great deal of what we take to be our condition.
What makes this bearable rather than bleak is the word anityāḥ - impermanent. This is not endurance of an infinite weight. It is endurance of something that is already leaving.
And note that he does not say the pain is unreal. That is a common misreading. Cold is really cold. It is simply not a thing that has arrived to stay.