What makes you so sure? (This is a serious question, not rhetorical.)
Myself I have a condition which 5-10% of people have. As a child, I had two very high quality psych evaluations for the time where people observed all the signs and symptoms (particularly the first one) but failed to draw a line between them.
Since then I saw therapists maybe 6 times in 30 years (sometimes the same one) and it was always “adjustment disorder with …” and there was some truth in that in that in each case I had some very ordinary kind of stress which was exacerbating my condition but in reality there was always a chronic aspect to that.
I’ve known numerous people who have severe mental illness (way worse than the quirk that got me kicked out of elementary school) and contact with the psychiatric system and never got a conclusive diagnosis. The first line for a lot of people is to see a primary care practitioner and get diagnosed with either “anxiety” or “depression” and prescribe the same medication in either case. A referral to an actual psychiatric nurse practitioner who is taking patients is almost impossible in 2023 in the US never mind an actual psychiatrist.
https://en.wikipedia.org/wiki/Rosenhan_experiment
This one is more positive but is checking that different diagnosticians get the same answer
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5980511/
and if that was applied to the "Thud" experiment you'd have poor diagnosis with a very high kappa (interrater agreement)