That's not true. Security is always a trade-off between effort invested and probability of a possible breach.

There is no 100% secure system.

This is not true though. Security is about mitigating threat at some cost. There are some threats you can't mitigate cost-effectively. Some are unmitigable at all.

its about layers which includes real security and sometimes trickery. the statement is true though about 100% and the attacker only once but some tack maybe would be in order. there are procedures that can reduce vectors and so minimizing damage and minimizing successes.