You can get the facts of a custom--like caste, and Suttee, and Thuggee, and so on--and with the facts a theory which tries to explain, but never quite does it to your satisfaction.

You can never quite understand how so strange a thing could have been born, nor why.
For instance--the Suttee.

This is the explanation of it: A woman who throws away her life when her husband dies is instantly joined to him again, and is forever afterward happy with him in heaven; her family will build a little monument to her, or a temple, and will hold her in honor, and, indeed, worship her memory always; they will themselves be held in honor by the public; the woman's self-sacrifice has conferred a noble and lasting distinction upon her posterity.

And, besides, see what she has escaped: If she had elected to live, she would be a disgraced person; she could not remarry; her family would despise her and disown her; she would be a friendless outcast, and miserable all her days.
Very well, you say, but the explanation is not complete yet.

How did people come to drift into such a strange custom?
What was the origin of the idea?
"Well, nobody knows; it was probably a revelation sent down by the gods." One more thing: Why was such a cruel death chosen--why wouldn't a gentle one have answered?
"Nobody knows; maybe that was a revelation, too." No--you can never understand it.