Why does it show that a person read a message on fb, but really didnt?

So think of it like a text message.
This has happened to me:

I'm texting with someone, and I put my phone on the counter without closing out of the conversarion screen.
I turn away to do something and I end up doing something else. Then maybe something else.

Now, because I didn't [i]close out[/i] of the text screen, when the other person replied, it didn't send an audible notification, and I havent looked at it, but on the other end it shows as 'read'

Then the phone screen 'times out' and closes on its own, and I don't actually see the text message until I open it up again.

This type of thing has happened on FB as well....so there's that possibility

[b]Or[/b], they just didn't feel like responding at that time and then lied. 😣

They did read it, but just decided to not reply... then lie saying they haven't read it yet..

Sometimes if they are on the web based application (computer) with the browser open on the messages it shows that it was read but in actuality they didn't physically open the message.

it could be they clicked on the message, which marks it as "read", but didn't actually have a chance to read it.

Maybe FB wants you to think they don't want to talk to you

They wanna mislead

It works sometimes, it doesn't work always. It only checks if your software has read it, not your eyes. That could happen many ways.