Why do people immediately assume ADHD/Autism on mental health posts?

Hi everyone, I’ve been thinking about posting this for a while because I’m genuinely curious about other people’s perspectives.

I go to therapy for things like anxiety, depression, and OCD symptoms, and I often browse different subreddits to see how others deal with similar struggles. One thing I’ve noticed is how often replies quickly jump to “this sounds like autism/ADHD.”

To be clear: I have nothing against autism or ADHD. I understand these conditions have been underdiagnosed for years, and for many people finally getting a diagnosis is incredibly validating and helpful. I also think it’s completely valid to share advice from your own experience.

The issue I’m noticing is when comments become insistent or dismissive, almost as if the poster’s actual experiences are being ignored. Sometimes it seems like people latch onto a tiny detail in a post—like noticing patterns or certain behaviors—and insist that it must be autism or ADHD, while overlooking the bigger picture. Many posters actively try to explore autism or ADHD themselves, sometimes taking screenings that indicate low likelihood, yet still get told they must be misdiagnosed or should seek another opinion.

What strikes me is that it often feels like the commenters forget that many diagnoses—including ADHD, autism, anxiety, OCD, or effects of trauma—can share overlapping symptoms. For example:

Someone noticing patterns might be autistic, but it could also be a coping mechanism learned after trauma, where they’ve trained themselves to spot patterns to anticipate danger.

Someone hyperaware of social cues might not be autistic—they could have social anxiety, causing them to constantly scan others’ facial expressions and body language out of fear of being a burden or saying the wrong thing.

Someone with OCD might create repetitive thought patterns as a ritual or to manage intrusive thoughts, or feel an intense moral responsibility that makes them overthink patterns and connections.

I’d love to hear other people’s thoughts on this. Have you noticed this in mental health communities? How do you navigate advice that crosses from “sharing experiences” into being dismissive, insistent, or overly confident about what someone must have?