Heinlein was critiquing (or at least lampooning) the use of the "competent man" in literature. It's what today we might call a "Mary Sue". The specific items o

Heinlein was critiquing (or at least lampooning) the use of the "competent man" in literature. It's what today we might call a "Mary Sue". The specific items on the list are not important. The point is that no one can possibly know how do to all those things. You might think you can, but you won't really know if you can die gallantly until the time comes. A more gentle interpretation of this quote might be aspirational; that the competent man is always improving and pushing his boundaries. I personally prefer that interpretation, but I don't think that is how Heinlein meant it.