And yet, you can't always swap a startup built with one's own hands with a bunch of others, just as one's child is not tradable for a bunch of other kids. Some founders might view their startups as pure investments, but I'd wager that more often than not, they view it as their child.

Startups are businesses intended to make money. Kids are kids. While you may feel an attachment to the former, there may come a time when selling is the best strategy. With kids, that's generally frowned upon.