To gain insight into what King means by "wait" in 1963's Why We Can't Wait, one could look to the history of the Civil Rights Movement and realize that after Lincoln's Emancipation Proclamation in 1863, the social and economic advances of African Americans moved at a glacial pace. Even after the 1954 Supreme Court ruling in Brown v. Board of Education of Topeka, complete desegregation was elusive. King points out that African countries were making rapid progress in social justice and shedding colonial oppression, while the United States dragged its feet.
In King's later "I Have a Dream" speech, he refers to the "tranquilizing drug of gradualism." It is perhaps the most descriptive metaphor for the "wait" for economic and social equality African Americans were enduring. The policy or principle of gradualism holds that small, incremental societal changes over a long period of time yield a desirable and perhaps more palatable result than rapid or abrupt change. King found this idea deplorable, as African Americans had suffered in America since the inception of slavery in the American colonies in the 1500s. Vague promises of slow, incremental change were not acceptable to King as the leader of a peaceful civil rights revolution. He and others believed that the "wait" for social justice must come to an end.