There is a temptation to link the anti-government demonstrations in Egypt with those that led to the fall of Tunisia's president. "First Tunisia, then Egypt" runs the refrain. But the so-called "domino effect" is too simplistic. It runs roughshod over the very real differences between the dramatic developments on the streets of Tunis, Cairo, and several other capitals in the region.
There is, however, a common source of inspiration that has empowered many of the demonstrators in different countries: the idea that after the government of Tunisia fell, people believe that they can bring about real reform after decades of stagnation. It is a moment of opportunity, but not without big risks.
Thousands of protesters flooded Cairo's main square on Tuesday night, braving water cannons and tear gas to demand reform. The demonstration was the largest the capital has seen in years, organised in part through a Facebook page commemorating a young Egyptian who was allegedly beaten to death by police last June in Alexandria.
While Egyptians, like Tunisians, complain about heavy-handed rule, Egypt's demonstrations cannot be understood as a knock-on effect of Tunisia's uprising. The reality is that discontent has been simmering in Egypt for years and for its own domestic reasons.
Opposition groups have been excluded from recent elections. The most powerful of these groups, the Muslim Brotherhood, which the government blames for the latest violence, remains a powerful opposition force despite its official ban. Until the Brotherhood and other opposition groups are brought out of the wilderness and into the political tent, the protests in the streets are likely to continue. By appearing to renege on a promise to hold fair elections last November, Egypt missed an opportunity to defuse tensions that have been heightened by rising prices and rising unemployment.
Egypt's security forces, and its government in general, are more experienced and organised than Tunisia's, though they will be tested by these demonstrations.
The most prudent policy - restraint - often seems to elude authorities. Yesterday the Egyptian government banned demonstrations; on Tuesday, social media websites were blocked and mobile phone services restricted.
If Cairo is to stem these protests and this decline, politicians, not the police, must be the ultimate line of response to Egypt's people. There is a sense that positive change is possible through peaceful demonstrations. Whether in Tunis or in Cairo, now is the chance for governments and politicians to show that they are listening and can lead that change.