Think about this for a second: As a manager, what's something you've had to tell an employee that you thought was surely common knowledge?
When managing people, your success is largely dependent on getting work done through other people. If they fail, you fail. In fact, you’ve failed twice because not only are you not delivering on larger objectives, you’ve also failed the employees that report to you because you’ve not given them the tools, training and mentorship they need to be successful in the first place. When your team drops the ball, the first thing you should do is look in in the mirror and critically / honestly evaluate your actions to see if you gave as much as you could to the cause. Many more times than not, there is more that you could have done, and a large majority of the time, it revolves around communication.
Managers are forced to juggle other people’s personalities, priorities and work styles. The only thread that weaves it all together is what you’re communicating and how your communicating it. If you’ve got an expectation of performance - you need to tell people. If you’ve got business goals - you need to articulate them in a meaningful way. If you have a process that needs to be followed - you need to explain and train it.
Never take what could be assumed as common knowledge, like showing up on time for a shift, and simply believe people will meet your expectation. This example alone has different meanings for different people. So, if “on time” for you is an employee who has swiped in and is standing at their work station at the scheduled start time, you need to communicate this - and hold people accountable to it. If your employees are always a few minutes late to their work station because “on time” for them is when they walk in to the building, then you’ll constantly be frustrated and chasing this issue. It’s pretty hard to hold someone accountable to an expectation that isn’t communicated.
There are countless examples of what may seem to be common knowledge, however there wouldn’t be a need for the saying “It’s common knowledge” if everyone followed the same practices around each example. Never assume people understand your expectations, no matter how trivial the situation may appear. Explain what you want and hold people accountable to it because an unenforced expectation won’t be seen as important and you’ll be right back to square one.