The single worst thing a manager can say is: "I assumed..."
It isn't the job of managers to assume. It is their job to ensure.
- To ensure that the people who are tasked to do the work know what is expected of them.
- To ensure that the people who are tasked to do the work know how to do what is expected of them.
- To ensure that the resources required to deliver the work are available when they are needed.
- To ensure that there are ways of means of making sure that the work is being delivered.
- To ensure that there are ways of means of determining when the work has been done.
- To ensure that there is a review process so that if the work needs to be done again it can be done to at least the same standard, if not better and more efficiently.
Every one of these points requires effective communication between the manager and the staff. Effective communication isn't just telling somebody something, or sending them an email, and then walking away expecting things to be done the way you want them. Communication is a game for more than one player. You need to listen. You need to ask. You need to check. Does the other person understand what you want? Do you understand what they mean when they're responding? Are you sure you know all the answers or have they got a better idea? Are you having an argument because they don't understand you, you don't understand them, or that you were talking out of the seat of your pants in the first place (oh come on, be honest, we all do sometimes).
Don't assume that questions and challenges are a bad thing: if your point of view doesn't stand up to internal scrutiny like as not it won't survive an outsider's inquisition. A tested proposition is a safer proposition.
So a good manager ensures that there is a conversation. And ensures a common goal. And ensures a fighting chance of success.
And a bad manager assumes that success will just come to them and that it's somebody else's fault if it doesn't happen.