The first successful overthrow of an Arab leader by his own people since the colonial era ended is a warning sign to many of the region's autocrats that their grip on power is no longer assured.
They will insist that their situation is not like Tunisia's: Egypt's Hosni Mubarak will believe that his troops will be more loyal, and his people more pliant, than those in Tunisia. Libya's Muammar Gaddafi will assure himself that his ruling philosophy and publicly modest lifestyle have earned him the people's love, unlike the enmity with which Zine al-Abidine Ben Ali, Tunisia's former president, was regarded. Algeria's and Syria's leaders are counting on recent memories of civil wars or brutal suppressions in the aftermath of past democratic disturbances to keep their people quiet. The oil sheikdoms, mixing strict Islam and relative prosperity, will consider themselves special cases.
And at this juncture, it is still unclear the extent to which Mr. Ben Ali's removal was a military coup under the guise of a popular revolt, and whether the new President, Mohammed Ghannouchi, will pursue needed political and economic reforms and cede power in 60 days, as he has promised.
But news of what happened in Tunis on Friday will reach dissidents in all of these other Arab countries - their leaders have not perfected the art of media censorship - and it is to be hoped it embolden others to take their private dissidence public.
Many Arab countries share the core problems that helped fuel Tunisia's revolt: insufficient economic growth; cynically manipulated elections; and political support bought through subsidies for food and gasoline.
When they try to liberalize without altering the character of the state, the result is unrest, as Egypt, in particular, knows from recent experience. But by doing nothing, they also risk unrest.
The unlikely catalyst of Mr. Ben Ali's downfall was the self-immolation of a simple street seller, pushed around one too many times by state security forces. This is not the way it was supposed to work in the Arab world; ordinarily, the death of Mohamed Bouazizi would have been a footnote. While the region is still dominated by authoritarian leadership, Mr. Bouazizi's fellow Tunisians may be starting to change the rules.