Cause-and-effect assumes history marches forward, but history is not an army. It is a crab scuttling sideways, a drip of soft water wearing away stone, an earthquake breaking centuries of tension. Sometimes one person inspires a movement, or her words do decades later, sometimes a few passionate people change the world; sometimes they start a mass movement and millions do; sometimes those millions are stirred by the same outrage or the same ideal, and change comes upon us like a change of weather. All that these transformations have in common is that they begin in the imagination, in hope.