How do you know the difference between fear and anxiety? …between specific and generalized anxiety? …between distractibility and ADHD? …between inattentive and hyperactive forms of ADHD?
How about the difference between anxiety and ADHD?
The lines might be both clearer, and fuzzier, than you’d expect.
There are diagnostic websites all over the place, including Wikipedia, but I generally prefer the (…slightly…) less horrible/catastrophic approach as in websites like Very Well Mind.