Chemistry. Water heats 1°, 2°, 99° — nothing dramatic. At 100° it erupts into steam.
Physics. Bend a beam. It springs back, springs back — then snaps. No warning. The stress was accumulating in silence.
Biology. A resting neuron ignores small nudges. Cross one voltage line and it fires — full signal, no half-measures.
Computer Science. A system runs fine at 90% load, 95%, 99% — then one more request and it collapses entirely.
Psychology. You tolerate, tolerate, tolerate — then one small thing breaks you. It wasn't small. It was the 100th degree.
Wealth and habits. Saving feels pointless for years. Then compounding crosses a line and money makes money faster than you can. Same with skill.