If you’re knowledgeable about something you are able to make up your mind about it. Other people can too, of course, but you are able to do it more efficiently and with greater accuracy than people who don’t know as much. Within your area of expertise, when faced with a situation, you are able to make sense of it; when faced with a set of materials, you are able to discern their meaning. You simply understand such things better than ignorant people. Your knowledge allows you to quickly and precisely form a belief. And, when pressed, you can explain how you know this. You have justified, true beliefs and an ability to acquire more of them.
But how can you develop this ability to make up your mind? Well, how did you become knowledgeable about your subject? The very general answer is experience. Experience, after all, is not just a series of things that happen to you; experience is an ongoing process that teaches you how the world works. You’re only really having an experience if you are making judgments about what is going on, forming beliefs about it. These judgments will not always be correct. The beliefs you form will not always be true. But you go on, forming beliefs and discovering them to be right or wrong, and moving on to the next thing. What matters, however, is to reach some kind of decision, some kind of conclusion.
Students are prone to getting quite philosophical when you tell them they should be forming justified, true beliefs. “True?” they balk. “There’s no such thing as truth!” This is why I like to begin with the very ordinary experience of discovering that you were wrong. You meet someone and form an opinion about their trustworthiness, favorable or unfavorable. A few week’s later you have an occasion to act on the basis of this belief. You trust them, or you don’t, and things, let us say, go badly. Your belief has been tested, and you come away from the whole experience with a little more knowledge about the person in question. You also come away a little wiser: you’ve had another experience with falsity. You know a little more about what it means for a belief to be false and, therefore, what truth is. You don’t need to be more sophisticated than this “for academic purposes”. (Unless your field requires it, of course. Philosophy is an academic discipline too!)
What is perhaps much more important is your ability to justify your belief. Why do you think it is true? Can you provide a compelling account of your reasons for believing something to be the case? Does that account jibe with what else is known on the subject? Do you appeal to hunches or prejudices or personal authority when supporting your claims? Or do you leverage evidence, explanations, counter-arguments? Do you understand what must also be the case in order for your belief to hold up? Do you understand what would have to be the case for you belief to be true? You may believe it very firmly today. But can you describe conditions under which you’d abandon the belief tomorrow?
Notice that all of this suggests something you can do several times a day. Pick a subject. Or even just read a few pages from a book. Make up your mind about what is going on there. Form a belief about it. Then go on with your day as though your belief is true. When talking to people, assert it confidently (if you’ve made up your mind then you can be confident.) Watch how people react. Notice what happens when you take actions that presume it is true. Do those actions succeed? Does your belief make you experience more predictable? Or does it cause you to be constantly surprised and frustrated? Return to the basis of your belief. Examine the sources. Does your belief need to be revised? Like the man says, it’s a process.
Update 20/10/18: I just tweeted a pretty good summary of this post: Knowledgeable people are better able to make up their minds (about the things they know something about) than ignorant ones. “Better” here means both more efficiently and more accurately. Their intuitions are sound and their reticence is necessary.
That is, knowledgeable people are able to make snap judgments in pressing situations, and these judgments will be more reliable than those of ignorant people. (Both may be right or wrong; but one of them is merely guessing.) But a knowledgeabe person will also feel the pull of doubt more precisely than an ignorant person. So in situations where there is time for reflection, the knowledgeable person will suspend belief where an ignorant person may rush to judgment. Finally, the knowledgeable person will often err on the side of reason. The ignorant person is free to follow their passions. (Or perhaps more accurately: their passions are free to have their way with them.)