LONDON — Brazilians have an expression, “Vai acabar em pizza.” Something that ends in pizza is something that ends in a big zero, zilch, nothing. The phrase is commonly used for the predictable conclusion of judicial investigations of the white-collar crime practiced with impunity by rich folk in Brazil.

Impunity is one of the issues driving mass protests across Brazil that began with anger over fare hikes. A pattern has emerged. From Sidi Bouzid in Tunisia — where a squabble over a fruit-and-vegetable cart ignited the Arab Spring — to Istanbul — where an uprising was triggered by plans to build a mall over a city park — these eruptions with hashtags share characteristics:Small spark, large conflagration; disoriented leader, leaderless movement; vertical rigid state power, flat nimble protests; harsh authority, impish youth; force of the state, flexibility of Facebook; police crackdowns, agile regroupings; conspiracy charges, humorous ripostes. Fidel Castro spent years in the Sierra Maestra preparing his revolution. Twitter has dispensed with that.

Or has it? A core issue with these social-media driven movements is, in the words of Zeynep Tufekci, an assistant professor in the School of Information and Library Science at the University of North Carolina, “How do you get from a ‘No’ to a ‘Go?”’In other words the eruptions whose shared slogan might be “Enough is enough!” are good at protest and resistance but much less good at defining objectives — whether political, social or economic — and organizing to attain them. They thrill in the negative. They tend to fizzle in the affirmative.

They lack leaders. There is no truck with a microphone. Agendas read like a Twitter timeline — fascinating but diffuse — rather than coherent expressions of a goal. There is no Martin Luther King or Nelson Mandela — or Tancredo Neves and Lula (among others) leading the fight for Brazilian democracy three decades ago.

As Wael Ghonim, the former Google executive who emerged as a significant, but not defining, figure of the Egyptian revolution, once put it on 60 Minutes, “Our revolution is like Wikipedia, O.K.? Everyone is contributing content; you don’t know the names of the people contributing the content.”Of course, from Tunis to Cairo there was a clear objective: the ousting of a hated despot. It was only after this unifying goal was accomplished that the weaknesses of a leaderless movement became apparent and groups that did boast organization — like the Muslim Brotherhood in Egypt or Ennahda in Tunisia — filled the vacuum. They have not, however, been able to satisfy the thirst of their nations for renewal.

In Turkey, Prime Minister Recep Tayyip Erdogan wanted a mall over the Gezi city park. The tweet went out with the hashtag #direngezi — Resist Gezi! Erdogan has befriended an oligarch, favored him with the usual lucrative networks, and this oligarch owns a popular chain of steak restaurants. Hashtag #direnentrecote — Resist entrecôte!The movement morphed into a lot of things by the time police drove out the occupiers of Gezi. It was about the autocratic turn of a conservative leader in power for 11 years. It was about Erdogan’s invasion of Turks’ personal lives, the way he calls them alcoholics if they drink, or advises them not to kiss on the subway, or comments on their dress. He is not the Sultan!It was about his deadening control of the media, and the way his Justice and Development Party, having opened Turkey up, now sees enemies everywhere. It was about how Erdogan’s push against the secular Turkey of Mustafa Kemal Ataturk has overshot: If there is no reason why a religious young woman should not attend college wearing a veil, equally there is no reason for the ruling A.K.P. politicians to rant about Muslim women in bikinis. Enough is enough!In Brazil the ire is more directed at the entire political class than President Dilma Rousseff herself. It is about the way politicians live like mandarins with immense privilege, their vote-buying scandals and their lack of accountability. It is about the skewed use of resources: more than $13 billion on new stadiums and preparations for the 2014 World Cup while basic health and education and transportation needs remain unmet. It is about police violence when acquiescence to injustice ends.

These movements have erupted in two of the major emergent powers of the 21st century where economies have been growing fast. I do not think this is a coincidence. Ordinary Turks and Brazilians, particularly young people, are reacting to a feeling of global forces beyond their control; they are reminding leaders swept up in boom times of the need for consultation and accountability; they are telling the hyper-connected financiers who have profited most that social justice — society itself — matters. By gathering, by occupying, they are asserting a shared humanity against atomizing development and the globalized shopping mall.

Can they get from “No” to “Go”? It will take organization on a scale not yet seen, decisions on objectives and, yes, leaders. But I do not see it all ending in pizza. From Tunis to Istanbul, from Cairo to São Paulo, something essential has already happened. Fear has fallen. That in itself is a game-changer.