Insanity is said to be hard to define, but I thought of one last night that I thought was a steel trap.
A person is insane when a correlation cannot be made by their community between their desires and their actions.
-The definition that a person is insane not when they run into a brick wall, but when they get up and do it again is a subset of this definition. The community at large cannot correlate a desire that would cause a person to want to run into a brick wall after having been seen hurting themselves doing it the first time.
The problem with this definition is, however, is that this would classify marathon runners and athletes insane as well. Since they continually punish themselves physically as well.
I assume you mean disadvantageous for the one with the mental state. What is the time frame for the disadvantageousness to take effect? Cigarrette smoking - and attendant addiction - fits the definition above, for example.
There would be very few insane people then, since questioning most people will find their rationale. And I would guess many sane people - by most people’s judgment - would do things that the community could not understand the motive for, at least without a thorough interview. And even then most of us have idiosyncrasies that we’d have trouble explaining. Or we should have trouble explaining, despite whatever rambling ideas we tossed out when questioned.
Further many people do things but are not aware of their real motivations - to show their father they have what it takes, to get laid, to not feel like a loser - and have official stories, which they believe, that are not correct.
Insanity: When one’s mind can no longer interact with 3 Dimensional reality that their external self does. Their mind, for what ever reason, whether it be by electromagnetic frequency variation (their brain is connected elsewhere) or the physiology of their brain itself has been damaged, hampering their ability to rationalize nor accept the world around them.