Psychology has the sizable problem that everything is a disorder but very little is actually known about any of them.
You can't say "ADHD is this" and point at a definitive cause, tis just a bag of related symptoms that is geared more towards consistent diagnoses (i.e. you go to five different doctors and they all diagnose the same thing) rather than attachment to a common underlying cause or consistent treatment plan and success phase.
This isn't to say psychology is useless, many people find great help in it... but when it comes down to it, it is scientists (who as a whole have some of the biggest problems in being good at being scientists) trying to describe malfunctions of the highest abstraction on the most complicated class of things known to exist... and just scratching the surface.
The last D is for Disorder... it's a value judgment and the question does need to be asked: if something isn't causing significant problems, is it a disorder? The answer isn't clear cut and people are going to draw the line in the wide grey area in different places.
The solution must be neuroscience continuing to advance to higher levels and replacing the vagueries of psychology with justifiable cause and effect explanations. It is advancing but still a far way off.