Question about message send failure notification?

[Prznsugar]

I sent a text message to a friend a couple days ago. They didn't respond to it and I assumed they were too busy to talk or something. Now a few days later it shows up as "message send failure" and a red exclamation point on it when it didn't show that before. Why did it take so long to notify me? Also does it mean they never received it or is this some kind of error?

 

[garirry]

Probably an error. I suppose that it was trying to send the message all this time, but it couldn't after that much time, gave up, and send you the failed notification.