Recent years have been tough on optimists. Hopes that the Internet might bring people together have been crushed by the ills of social media. Is there a way back?

Chris Anderson, the head of TED, believes that we can turn outrage back into optimism. It all comes down to reimagining one of the most fundamental human virtues: generosity. What if generosity could become infectious generosity? Consider:

• how a London barber began offering haircuts to people experiencing homelessness - and catalysed a movement

• how two anonymous donors gave $10,000 each to 200 strangers and discovered that most recipients wanted to 'pay it forward' with their own generous acts

• how TED itself transformed from a niche annual summit into a global beacon of ideas by giving away talks online, allowing millions access to free learning

In telling these inspiring stories, Anderson offers a playbook for how to embark on our own generous acts - whether gifts of money, time, talent, connection, or kindness - and to prime them, thanks to the Internet, to have self-replicating, world-changing impacts.