Whenever talking, stay on topic; don’t change the subject.
First, you must know your subject of discussion, which many people don’t. Second, understand that trying to change the subject is just as dangerous—yes, dangerous—as allowing other people to change the subject. But, if you don’t first know which subject you are discussing, then it’s hard to stay on topic at all.
People who change the subject either don’t know the subject much at all or know the subject all too well—and are doing it intentionally.
When answering questions at a Q&A, educated teachers will often begin their answer by explaining the broader subject that the question relates to, usually a section and row of books in a library. One of the best textbook examples is Ravi Zacharias. Every question relates to a topic that has almost always already been written about in exhaustion. People ask those questions, usually, because they may not even know that the subject itself exists. So, identifying the subject of the question is the first part to a proper answer.
When you say, “That employee does a bad job,” don’t accept the answer, “He worked here for 20 years.” It is not on topic. Your initial statement was about job performance; the response was about history, familiarity, defense of personal character, perhaps even cronyism or even nepotism; “He is my friend, my own son.” Of course, it might not be your place—you might not have enough information—to be accusing an employee of doing a bad job in the first place. In that case, a more appropriate response to your initial statement might be, “He has worked here longer than you.” In that case, it is you who are off topic—the topic of focusing on one’s own job performance.
By knowing your subject, you will avoid switching topics in conversation. That will help you avoid unnecessarily ugly arguments and to be resilient against populism. For this, it is good to familiarize yourself with “logical fallacies” on your own: red herring, straw man, emotional appeal, ad hominem, appeal to the stone, argument from ignorance, illicit minor, argumentum ad populum, appeal to authority, appeal to hypocrisy, and many more.
Proverbs 19:8, John 9