Because in your busy life, you have got very little time; therefore after gṛhastha life, fifty years, up to, not more than that, pañcāśordhvaṁ vanaṁ vrajet, then you must retire. It doesn't matter whether you have finished your duty or not. It doesn't matter. You must retire. And then, after being trained for sometimes, being retired from the family life, living secluded life—not exactly secluded, but detached from family life—let the elderly sons, daughters, they can take care of the family, and the husband, wife, they travel in different places of pilgrimage. Again they come for some time, but without any attachment, as guest in the house of his son. In this way, when he is trained up, then he says to the wife, "Now you live with your sons. They will take care of you. I am taking sannyāsa."
So everyone has to take sannyāsa. It is not that a particular man, simply Caitanya Mahāprabhu has to take sannyāsa. No. That is obligation. You must.