Some people have a knack for it, but even then it takes practice. The tools are logic, reason, and evidence. Does that sound trite? It should. But we live in a world where, e.g., a straightforward application of evolutionary biology to H. sapiens immediately yields conclusions which, if you expressed them in an American workplace, would compel your employer to reprimand or fire you. When reporting the results of logic, reason, and evidence can get you fired, the trite becomes the profound.

Those people you deride

I derided no one. Calling absurd beliefs absurd isn't derision.

are quite sure that when they know is true

You assume a false symmetry. They are mistaken. I know this the same way I know that creationists are mistaken. Creationists may sincerely believe they are right, but it's not ironic to observe their error.