1. Network problem
The network is bidirectional. Just because your network is good and the transmission is successful does not mean that the opposite network is good. If the other party has a poor network or no connection, he won't receive your message.
2. Version problem
If your WeChat version is too far away from the other WeChat version, it will also affect the reception of information, but this is an accidental probability, and there will be no problem every time. For example, yours is the latest version, and his is the version many years ago, so sometimes there will be big problems where the network card is. You sent a message, but he couldn't receive it.
You were disconnected at the moment of sending the message.
You edited the message and sent it, and then you immediately disconnected yourself. At this time, you showed that the transmission was successful, but in fact your message was not sent out, so the other party could not receive it at all.
I received it and don't want to talk to you.
The message was indeed sent successfully, and the other party saw it. I can't read it back. It's that simple. I don't want to talk to you after reading your message. I'll tell you that he didn't receive it. Let you think for yourself.
Wechat tip: If it is only once or twice, there is no problem. But if you often have this problem, you need to see if there is something wrong with your mobile phone. Try updating the version or restarting the phone. If you have time, it is ok to kill a virus.