As with everything education is paramount to understanding oneself and others.
To really have the “tools” one must have a good working knowledge of psychology, an understanding of pathology, an understanding of projection and how people, often, detest in others what they still need to work on, heal, within themselves.
We must know ourselves and our triggers and be on red alert for the stealth of ego. lol
These inner “clues” may not be reflective, in an exact way, bit they are pointers to those areas which still merit examination.
For instance, I detest liars, and while I do not, and have not, ever told a life altering lie to another, I might need to examine how I might lie to MYSELF, even in small ways, such as ” Oh, what the hell, you can afford to spend X amount of dollars on this”...can I, really, or am I being self deceptive?
As this “work” progresses it is then possible to notice lies and deceptions in others from a place of consciousness and rather, than feeling defensive from one’s own unhealed and unacknowledged issues, this behavior just simply, ceases to resonate within, and one can observe without reactivity.
It’s a LOT of work, and very few ever really take themselves to task.