Name-calling, attacking a person’s character and using someone’s beliefs or traits to call their argument into question. For example, you can’t say that someone’s argument about dogs being better than cats is weak because they are also a Republican. It offers no real support to your argument for cats being better and it makes it look like you can’t think of anything better than poking at their personal beliefs.
Becoming comfortable with uncertainty and not knowing is a vital step to becoming a better decision-maker. What makes a decision great is not that it has a great outcome. A great decision is the result of a good process, and that process must include an attempt to accurately represent our own state of knowledge.