London is one of the most densely connected cities on Earth — thirty-three boroughs, three hundred languages, and millions of small daily encounters between strangers on the Tube, on high streets, and in queues that somehow form themselves. It is a perfect substrate for a kindness chain.
Londoners famously do not talk to each other on the Underground, which makes any small act of kindness on a train wildly disproportionate in its impact. One coffee bought for a stranger at Liverpool Street can produce a chain that reaches Camden, Brixton, and Stratford by the weekend.