Definition of idealist, cynic, and realist

The book Getting Things Done: The Art of Stress-Free Productivity by David Allen has forever changed how I think about tasks, projects, inboxes, calendars, etc. Allen puts various quotations in the margins of the book. I was recently remembering this one:

An idealist believes that the short run doesn’t count. A cynic believes the long run doesn’t matter. A realist believes that what is left done or undone in the short run determines the long run. –Sidney J. Harris

(Quoted on p. 253)