[Continuation of why a person with good excuses will never attain the Torah he did not learn]
This is like a group of merchants who went to a distant market together for several weeks, and when they returned, they each started describing in detail how they made a small fortune. There was one merchant among them who came back empty handed, and even though his explanations and excuses prevented terrible humiliation, they did not make him any wealthier than before he left.
So it is with a person who is sent down to this world for a short time to amass eternal spiritual wealth. He must be very careful not to waste any time, for even a mediocre merchant can amass a fortune in this marketplace. He can learn Mishnayos, or simple halachas, because any form of Torah can sustain a person in the world of eternity. However, if he wasted his time in the marketplace, even if he had good excuses, he will not be able to reclaim his eternal loss.