"Success" is going to be exactly how Steve Peterson defines it. Bottom line.
I'm no defender of Solich, but the man got fired after batting about .750 +\- over his head coach career. Facts is facts. Peterson didn't think that was too successful.
So on we move to Callahan. I believe he's right at .500 +/- as we sit here right now, and will probably be below that mark after the CU game. While I'm willing to "give him another year" in my own mind, I believe that Callahan will never break the .500 mark as head coach at Nebraska, whether he's here 1, 2, 3, or more years. We are hopelessly out-coached most games. Facts is facts. Our talent (although it is generally minimized) will allow us to win a few home games per year, and perhaps one road game per year. We will have to rely on Mr. Peterson to determine if and when the sub .500 mark isn't successful.
However...I would surmise that Mr. Peterson's definition of "success" has probably been modified a bit since he's the one that grabbed ahold of the steering wheel.