I'd distinguish here between "difficult" as in requiring discomfort and "difficult" as in requiring optional effort. By optional effort, I mean effort that one could feasibly take the null action rather than exert. None of the effort expended in carrying a baby to term is really optional at the time. If I were to get pregnant, I could at no time say to myself, "Well, I'd really rather not vomit right now, so I'll take the null action." Even if there were something I could have done earlier to enable the null action at that time, once it gets to that point, it's happening whether I like it or not. Similar with labor. I don't think anyone will perform an abortion when one is literally about to extrude an infant, practically speaking, so although labor is an immense effort, it is not an optional effort once it's gotten to that point. Taking Plan B, going through with an abortion, and yes - mailing a check, are all optional effort.