It's different everywhere (let's leave the parochials out of this for now that's a different set of circumstances and should be discussed in isolation.)
If you walk into a Los Gatos, Palo Alto, Wilcox, Aragon, etc. and know what you are doing, you will have success. There is a history there, and there are people in that community with a vested interest in the success of the football team. The athletes are there waiting to be coached and the infrastructure (money, admin, boosters) is in place with a keen understanding of what needs to happen. If an admin happens to make a bad coaching hire at a place like this, there is direct community pressure to fix it....quick.
If you walk into a place that has not had historical success, you are talking about a total overhaul. You are not just coaching the kids, you are coaching the community, which probably has no concept of what winning looks like and how to help. In these cases there are many variables, but it's not impossible. It takes an iron will and a lot of help. In these cases admin is extremely important because they have to support culture changes that many people resist.