Are your reasons causes or press releases?
What it argues
In split-brain patients the left hemisphere produces confident explanations for actions initiated by processes it had no access to. Gazzaniga calls this the interpreter. The finding generalises: reasons are often generated after the act, and their fluency is not evidence of their accuracy.
The probe
Catch one explanation you gave today for a choice. Ask whether you had the reason before the choice or constructed it after.
The source
split-brain studies; The Ethical Brain — Michael Gazzaniga, 2005. The link goes to the text or to a catalogue record for it, not to a summary. This one is a catalogue record: the entry gives you the question and the probe, not the argument in the author's words.