"20% probability of rain" means if you go out on five different days when rain is 20% probable, you will get wet on one of them. But whether it's comparable to a lottery ("It could be you") or a meteorite strike ("We'll all go together if we go"), depends on the nature of the weather patterns being forecast. If showers are forecast, someone will get wet - it could be you. If a hurricane is approaching but its course is uncertain, either everyone will get wet, or no-one.