Let each of us please his neighbor for his good, leading to edification."
Romans 15:1-2 (NKJV)
Truth is absolute, but people's perception of the truth is not. It is true that if you add two of one thing to two more of those things you will have a total of four, that is the truth. But what if someone was very bad at math and they thought that two plus two is three, or five? That person may be convinced that two plus two is three or five, even though that is not accurate or true. The solution in this situation is not to start an argument or debate, but to find a way to show the person that the correct answer really is four.
Christians, and people in general, can have different ideas and perceptions of what is true and false. Unfortunately, what often happens is that people will argue about something, trying to prove that what they are saying is true. Very often the issue is not resolved and people only end up offended and upset, which is not the same as helping people and leading them to edification. Humility and kindness can go a long way in helping people see and understand the truth, without creating a problem in the process.
Some people believe that the main point is to show people what is right and wrong, and if they don't like it, then that is the other person's problem. But in Romans 15, Paul said that the "strong" people should not just try to please themselves, but work towards pleasing others and edifying them. There may come a point where we need to take a very strong stand for the truth, but that is not the first step in dealing with other people. We need to bring the truth to people in a way that will help them clearly see right and wrong, and that will lead them to being edified by knowing the truth.