Careful who you selfie-shame, you never know who you could be calling out.

Case in point, a woman named Brenna Mae  gained a lot of attention for a tweet she posted calling out a stranger who mocked her decision to take a selfie outside Trader Joe's.

While the stranger probably thought he was dissing a vain Millennial, Mae actually suffers from agoraphobia and was taking the selfie to celebrate the fact she was able to go out in public without fear.

Here's some context.

Agoraphobia is a mental health issue that often causes victims to "have a hard time feeling safe in any public place, especially where crowds gather," according to the Mayo Clinic. Given her condition, going to Trader Joe's was a pretty big deal and worthy of a selfie, but the stranger apparently told her that going to the grocery store is nothing to celebrate in photographic form:

@TheBreeMae Twitter - twitter.com

Mae, however, shared some strong words for her critic in an open letter on Twitter.

"I know what you thought you were seeing," Mae wrote. "Just a self-absorbed, shallow millennial, documenting a mundane task for no reason. 'Stupid kid,' you might have thought, 'not every little thing has to be documented. Put your phone away and get on with your life.' But here's the thing. I also know what you were unable to see: I am agoraphobic."

She wrote that for more than three years, she hasn't gone out in public alone:

@TheBreeMae Twitter - twitter.com

When she felt good enough to go to the store this morning, it gave her a lot of "courage," which the stranger shut down in a cruel way:

@TheBreeMae Twitter - twitter.com

Mae wrapped up by saying the stranger was present for a big moment in her life, yet unknowingly trivialized it by casting judgment:

@TheBreeMae Twitter - twitter.com

Mae, however, was met with a lot of support on social media:

One user who suffers from panic attacks related to Mae's anxieties:

Mae wrote that she was surprised by the overwhelming response to her initial tweet, and clarified that the stranger did not ruin her day:

[Ed. note] This subject of this article's name has been altered to to conform with her preferred online identity.