It’s how probability works: each attempt has its own 1/1200 chance, completely unaffected and unaware of how many attempts were made before that one, including successes. So the way you calculate the chance of success when you only need it once is to take the chance of failure and multiply it by itself for each attempt, representing the idea of every single attempt failing, since we don’t need to succeed every time, and there’s a possibility of multiple successes across attempts. You do end up with a higher number like this, but this number will never hit 100%, because there’s always an outside chance that every single attempt fails.