The problem

Friday, 5 p.m. The dev team sends you a tarball and a README that says "deploy to prod". Saturday, 2 a.m., the app falls over. Monday, the developers say "it works on my machine", and you say "it never worked on mine".

Both teams do their job. The devs are paid to ship features, and you are paid to keep things up. Most outages come from a change, so each team's goal works against the other's. Between you stands a wall made of tickets and handoffs.

DevOps removes that wall. You do not install it and you do not hire it. The people who build the service and the people who run it own it together.