What's with this error-messages?

Wanted to post a thread (!) just a thread OK and I was opening it I got the error message that I am not allowed and have to wait 30 seconds for "you just wrote a post" what the fuck why? Can anyone explain to me why this message exist? Also you don't even know how long it will take me to write and than publish something so it is just confusing to me to send me this error ...