Those with no abilities would become (unless they are totally self-deluded) quite depressed. I happened across a quote this week that explains how people can be happy in their work.
"In order that people may be happy in their work, these three things are needed: they must be fit for it; they must not do too much of it; and they must have a sense of success in it." -John Ruskin, author, art critic, and social reformer (1819-1900)
Of course, we now have many non-able, self-deluded people employed - they're in the government.