Be Competent, But Be Selective
Oftentimes early in your career, you will be faced with a new problem: choice. In school, you were given very few choices. You could select some classes and if you went to a university or college, you could select your major and even modify the electives a bit. But, in the real world, you will often be given many, many choices.
Specifically, in a job, you will be given choices that don't seem like choices. When you move up into jobs in engineering, program management, finance, operations, and other corporate positions, you will be given an ambiguous and often changing description of your tasks. Most of the time it comes with a to-do list that can never be finished.
You will never be done. Therefore, think of your competency as a resource you must spend.
(For a really good break down of how to think of this in a risk management style, read Reed Hasting's No Rules, Rules about placing bets on your job items).
Think about where you want to land and the impact you can have, less about the job description and the specific requirements when you interviewed.
At the end of the day, you are hired to make an impact for your employer, your boss, and your boss's boss. Do what makes the most sense to do that and you will be rewarded. Oftentimes, this means diverting your best mental effort to one piece over many.
Giving everything all the time is the path to burn out. So, be selective and drive results.