The effect of investing in security depends on the actual level of security achieved in the system. It also depends on the degree of trust from my stakeholders.
Imagine a system with perfect security which - for whatever reason - isn't trusted by those who should depend on it. Their distrust might appear totally irrational to us. That doesn't matter. It's not our call. Our effort is a failure.
Putting all our money into "actual" security and ignoring the need for assurance is a recipe for failure.