Dhīra means very sober. In the beginning Kṛṣṇa said, dhīras tatra na muhyati (BG 2.13). Dhīra means one who is sober. He is not bewildered. So dhīra means that although there is cause of disturbance, one is not disturbed. Although there is cigarette, but I should promise, "I shall not smoke." Although there is facility for illicit sex, I'll not do it. That is called dhīra. Dhīra means the cause of agitation or disturbance is present there, but one is not disturbed. So in order to advance in spiritual life we have to become dhīra. And that is said here, sama-duḥkha-sukhaṁ dhīram. As soon as one become dhīra, sober, these so-called material pains and pleasure does not disturb me (him). Then he is fit for becoming immortal. Everyone is immortal, but he is fallen in such material condition that he thinks himself as mortal. Because I am spirit soul, therefore the Vedic injunction that feel:(?) ahaṁ brahmāsmi, so 'ham, means "I am as good as the Supreme Being," means "He is eternal; I am also eternal. He is also living being; I am also living being." That means qualitatively we are one, God and me. But quantitatively, He is great; we are small.
So we have to realize this, that we can become eternal, immortal, all qualified like God, if we get out of these material clutches. And for this, we have to become dhīra. Dhīra means, I have already explained, not to be disturbed, even the cause of disturbance is there. So that is the qualification of becoming immortal. So little tolerance of the sensation... Just like there is some sensation. If you have got some itches and you are feeling that "I should itch," but if you stop itching, this will be cured, and if you go on itching, it will increase. So itching... Anyone who has got some experience of itching... Itching is very pleasing at the time of itching, but next time it is not very pleasing. It has created so many disturbing condition. Therefore śāstra says that we should try to control the itching of our senses. Then he is dhīra. And as soon as you become dhīra, you are the first-class candidate for going back to home, back to Godhead. So there is method; there is practice; there is process. If you like, you can adopt them—actually there is no difficulty—and solve all the problems of your life. This is Kṛṣṇa consciousness movement. Try to understand and adopt it.