The truth is usually shorter than the lie.

Something that happened needs no construction. You describe it and you are finished, because the details already hold together and nothing has to be checked against anything else. An invented account needs support, which is why it keeps growing, adding reasons and timings and extra people to hold up the part that is not real.

Use length as a signal in both directions. When your own explanation starts to expand, notice that and stop. When someone else’s does, you need not accuse them of anything, just hold the question open a little longer.