Two videos, same creator, same effort. One gets 300 views, the other 3 million. It looks like luck — and partly it is — but underneath is one simple number that decides almost everything.
A chain reaction
You post. A few people see it. Some of them send it to friends, who send it to theirs. Like a nuclear chain reaction or a virus, the question is: does each “generation” get bigger or smaller?
Post it into a crowd
Try 4 people × 20% (K = 0.8), then 4 × 30% (K = 1.2). Press “New crowd” a few times — luck matters too.
K-factor = 4 × 20% = 0.80
fizzles out 💨generation 0 · reached 1 / 112 people
The K-factor
K = shares per viewer × chance each share converts. With K = 0.8, 100 first viewers bring 80, then 64, then 51… the total stays limited (about 500). With K = 1.2: 100 → 120 → 144 → 173… it keeps growing until it runs out of people.
Virality isn't a big number. It's a number crossing 1.
Quick check
Each viewer shows a post to 5 people and 10% of them share it again. Will it spread by itself?
Levers you control
- Emotion: awe, humour, surprise and “so true” relatability make people share.
- Identity: people share what says something about them (“this is so me”, “my profession gets it”).
- Usefulness: “my friend needs this” — tips, tools, warnings.
- Low friction: short, clear, understandable without context or sound.
- Social currency: being the first to share something new or insider-ish.