If something is 20% likely to happen, is it 100% after 5 times?

The belief that an event with a 20% probability becomes certain after 5 occurrences is a common misconception in interpreting probabilities. Each event is an independent occurrence, meaning the probability does not increase cumulatively with each repetition but remains constant each time. As explained in the Huberman Lab, when attempting conception with a 20% success rate per attempt, it doesn't guarantee success after five tries. The probability of conceiving remains 20% each attempt, as each event (like each month trying to conceive) is independent of the previous ones. This lack of cumulative increase in probability keeps the chance of success in each individual occurrence unchanged, even though attempting more times might increase the overall likelihood over time due to more opportunities 1 2.

Therefore, no, a 20% chance does not become 100% after 5 occurrences. Each occurrence still only has a 20% chance of happening.