After 18 days of historic protest, Tahrir Square has finally found reason to let off fireworks and brighten Cairo's night sky.
It seems an unnecessary cruelty to cast a shadow over the massed crowd when they have secured what is certainly the most far-reaching change in the Arab world for many decades.
But this is a revolution that has stalled every time it appeared at the cusp of takeoff, and Hosni Mubarak's departure does not yet complete the victory for Egypt's democrats.
Within hours of the moment, Egypt's finance minister appeared on television to promise that "the oligarchy" would be swept away too.
But for six decades, civilian and military elites have deeply inter-penetrated.
The army has hedged its bets in masterful fashion over the last two weeks, appearing to side with protesters but remaining passive in the face of regime-sponsored violence and accepting Mubarak's desultory promises of reform until this was no longer tenable.
This is because the military establishment stands to suffer enormous losses, in both financial and political terms, from genuine democratic reforms.
Moreover, if a future government seeks to chart an independent policy towards Israel or Hamas, the military will be loath to jeopardise its flow of US aid.
This could prompt a Pakistan-like situation in which elected leaders are stripped of control over foreign policy.
The man now at the apex of Egypt is Defence Minister Mohamed Tantawi. He embodies the reactionary forces still embedded at the heart of a regime that may have shed its figurehead but not its essence. Field Marshal Tantawi is known by junior officers as "Mubarak's poodle".
According to Wikileaks cables, he has resolutely "opposed both economic and political reforms that he perceives as eroding central government power" - hardly such stuff as revolutions are made on.
There is every possibility that he will simply rebuild the apparatus of autocracy by dispersing superficial powers to a fractured opposition, while restoring the army to its Cold War standing.
Some optimists have invoked the "Turkish model" for Egypt, but recall that the Turkish army has toppled four governments since 1960 and still lurks just under the surface of that country's democratic institutions.
Surely, though, American pressure will push military elites, with whom they have extensive ties, along the path of reform?
President Barack Obama noted on Friday night in typically florid style that "the arc of history has finally been bent toward justice".
Perhaps, but for most of the past two weeks Washington has been chasing that arc from a safe distance. When the regime seemed to have locked in army support, the White House went silent.
What has united observers as disparate as Iran, Hezbollah, Britain and the United States is a frantic and flimsy effort to catch up with the crowd's indomitable spirit.
Just as Iran claimed the uprising as an Islamic revolution, Mr Obama clambered to put the US on the right side of change.
There is little reason to suppose that Mr Obama's lofty demands will be backed with the force of America's weight if the administration thinks that the old guard will continue to call the shots on matters of US concern.
'Strewn with traps'
Germany's Angela Merkel reacted to Mr Mubarak's ouster by demanding that "future Egyptian governments… uphold peace in the Middle East and respect the treaties concluded with Israel".
This is not unreasonable, but it indicates the low priority placed by the international community on the democratic quality of future Egyptian governments.
As in both Lebanon and Palestine over the past six years, democracy promotion could wither on the results of future elections.
The ill-informed alarmism about the Muslim Brotherhood that has accompanied these protests does not bode well.
Finally, even if the military hands over power to a broad-based opposition committee and steers through far-reaching reforms, the path to democracy is strewn with traps.
As the revolutionary high subsides, the social pressures that kicked off unrest will pummel an inexperienced and fragile government.
But instability has inflicted grave damage on Egypt's economy, which was already in precarious fiscal shape.
Demands to increase food subsidies will combine with extended disruption to tourism. If the government cannot pay workers and ensure social welfare, it is likely to be anti-democratic forces that are the beneficiaries of a backlash.
There is a fine line between realism and cynicism, and Egypt's would-be democrats have supplied reasons for hope.
These include the remarkably broad-based nature of the protests, to the scenes of Christians and Muslims protecting one another from police violence during prayer.
Mass mobilisation has forged new political forces in Egypt that will make themselves felt in any democratic future.
But the heat and light of revolutionary successes can obscure the scale of the challenges that must follow.
When the fireworks have stopped, Egypt's crowds must sober up if they are to redeem their promise of post-Mubarak freedom.
Shashank Joshi is an Associate Fellow at the Royal United Services Institute (RUSI), a defence think-tank, and a doctoral student of international relations at Harvard University.