This isn't true. Reason always has to start somewhere, which means that the starting point must necessarily NOT be reasoned into. You can only reason with someone who shares some presuppositions with you, which is why reasoning always begins with searching for those shared presuppositions, and then reasoning forward from there.

Read Plato's Socratic Dialogues and you will see someone who starts with the unreasoned assumptions of common sense, and then reasons backwards to change them. That is how dialectic works, and it's goal is to find a set of shared assumptions that can be the starting point for reasoning forward. More on this here:

https://www.academia.edu/43960326/Science_Reason_and_Agnosticism