There are several things that destroy your ability to be effective. Thinking you have all the answers (which leads to stopping learning) is probably at the top, along with any other reason for stopping learning (more interested in other things, etc.).
How you are taken by people is also very important. If people see you as talking down to them, it is very difficult to have them listen and care about what you say. At the same time I find it even more annoying when people refuse to say something that will annoy anyone (especially in responding to questions). You don’t want to talk down to people, but it is perfectly all right to challenge them. You need to respect them and challenge them to improve how things are being done.
Look at people like Ackoff and Deming. They knew more than pretty much anyone about management. Yet both continued learning until the day they died. They were quick to credit others. They were quick to challenge people but also had an obvious respect and compassion for people.