Pr[something happens across 1_000_000 events]
= 1 - Pr[nothing happens across 1_000_000 events]
= 1 - Pr[nothing happens once]^1_000_000 ## assuming independence
= 1 - (1 - Pr[something happens once])^1_000_000
= 1 - (1 - 1/1_000_000)^1_000_000
≈ 1 - 0.378
= 0.632
It's still below 99% for 4 million ops.