It's extremely expensive. Many banks and companies in the finance industry (hedge funds) do this:

Hire at least 2 or 3 people for every job. Have them watch each other whenever touching systems that connect to production or deploying code to production. Never trust any one of them with the private keys or passwords to anything - they can only get half of a secret and their co-worker gets the other half.

To do this effectively, you have to build a zero trust environment, and rely on surveillance to ensure that nobody is a bad actor. It really makes CIA/NSA level security look somewhat weak.

It's also very expensive, as you can imagine.