We like to tell people what we know. I don't know the exact psychology behind it, but my guess is that it has something to do with wanting to be seen as smart. When interviewing people, all the questions asked are to find out what they know. We are looking to see if they know how to communicate, how to solve problems, how to address conflict, etc.
A healthy exercise for any manager is to ask themselves "what don't I know?"
Note: Don't ask your employees to do this exercise. This question can be intimidating when asked by a boss.
The simple fact is there are lots of things you don't know. Our brains and experiences don't allow us to know everything. What will make you a good leader is knowing what you don't know and admitting it. Then you can ask for help. Then you can find an expert or a coach. Then you can grow.
The curse of this question is THINKING YOU KNOW. A great experiment for any manager. Write down the tasks you think an employee does during the day. Be as specific as possible. Make sure you write down what you think they do, not what you want them to do in some distant, perfect state.
Then ask the employee to do the same. Tell them to be honest and this isn't about checking up on them or trying to trick them. Tell them simply that you are testing yourself.
When you compare those lists, most managers will see huge disparities. You may think they are doing some deep thinking about problem solving and the employee actually is doing administrative work or answering phone calls from clients. Don't be surprised if their list is twice as long as yours. Most employees do countless things every day of which the manager is not aware.
Most managers have no idea what their team does on a daily basis - which isn't bad, it shows you are giving them autonomy. However, your team sees it as a sign of disrespect that you don't know. They don't feel valued or important. This creates disengagement.
You can't be self-aware unless you can figure out what you don't know.