Critical mass
A threshold at which a system jumps phase discontinuously.
In physics, a critical mass is the amount of fissile material needed for a sustained nuclear chain reaction. Below it, nothing self-sustains. At or above it, the reaction takes off.
The threshold dynamic shows up everywhere. Water boils at 100°C, not at 99°C. Network effects kick in once a platform has enough users; below the threshold, nothing. Viral content needs a critical density of sharing; without it, the content dies; with it, it spreads exponentially.
For operators, the practical implication is sharp: the last unit before the jump is wildly more valuable than the rest. Getting from 0 to 9,999 users matters far less than getting from 9,999 to 10,001 if 10,000 is the threshold. Most startups die just below their critical mass.
Examples in the wild
Marketplace businesses need critical mass in supply and demand simultaneously. Below the threshold, both sides give up. Above it, the marketplace self-sustains.
Viral products often look terrible for 18 months and then suddenly take off. The threshold dynamic is what produces the hockey stick. Investors who pull funding 80% of the way to critical mass kill what would have worked.
Many fitness, dietary, or skill changes show no result for weeks, then suddenly compound. The critical-mass point is what determines whether you quit too early.
Critical mass is one of the mental models we apply through real cases inside the Pareto MBA — a part-time program for professionals who want to think clearly about business.