To be precise, your College diploma will not prepare you in the slightest for any of the multitude of skills you actually need in the job market nor is it designed to do so.
That's a bit short-sighted. Yes there are theory heavy classes that don't translate, but there are many classes that teach you essential skills that are necessary in the real world.
For example finding vanadium contamination, you'd know from a metallurgy class one of its uses is to harden steel so it narrows down areas to look at. Knowing how to modify reflow temperatures to get the desired grain structure is essential in many applications to get the necessary bulk properties. As is realizing a component of one chemical you are using is interacting with another and damaging what you are trying to do.
You may not always need those things, but they are part of your intellectual toolbox and are essential when you find yourself trying to solve real world problems. Especially when time is of the essence and you don't have time to learn these things on the fly.
It doesn't even have to be something that you were directly taught in class, but having the background can help you make intelligent assumptions to further investigate and design experiments to determine the solution.
You also never know what is relevant to your interests. I never cared about world politics or contract law, but when you're put on a project where you're negotiating business deals, participating in a symposium on RoHS, or trying to understand the political implications of conflict metals, the world becomes larger and more complex.
As I said before there's a lot of things I never used, like knowing the switching speed of GaAs is faster because of the smaller band gap and lower effective mass of an electron. But you never know when an esoteric concept comes up and it's helpful to have a well rounded background, especially if it's in the field your diploma says you're an expert at.
Every successful person has had failures but repeated failure is no guarantee of eventual success.