[jkxyz]

I'd say that's why diagnoses are typically a "perfect storm" of otherwise normal conditions. We can probably all say that we've experienced schizoid avoidance patterns. But at some point, for certain people, that condition becomes a part of a larger psychological pattern in which it's considered an illness. Usually because it begins to have an overtly negative impact on the ability to function in society.

The nature of human development just means that we all inherit some level of personality "defect". But psychologists don't view them all as candidates for a diagnosis of mental illness.