Why?
Once a person gets over the newness of carrying, it is actually quite easy to forget the firearm's presence or the need to disarm for whatever reason (no-carry areas, etc.)
The primary focus is no longer on yourself or the gun - nothing strange or unsafe there. Just need to pay attention to remember the stupid laws and/or those policies you choose to follow.
if you forget you're carrying, then it seems to me that your ability to use said weapon is zero. Situational awareness?
Have you ever forgotten you were carrying while doing so openly?