Just say “I don’t know.”
It’s a lot better than feigning certainty about something presented without evidence, or making something up and declaring it to be true.
- Yes, I am including religion in this.
- Yes, I am including anything that could start with “you know what I think?”
- No, I am not including things that the scientific community resoundingly agrees is true based on experimentation and evidence.
The point isn’t that all theories and beliefs are false. It’s that it is an objectively more accurate way to go through life to dig in about things based on evidence, than it is to construct a model of reality around things without objective, falsifiable truth.