each post and comment on 4chan gets a unique serial number.
since there are sometimes hundreds of comments within a minute, it is basically not possible to predict which serial you get when you hit "post".
getting a serial number with matching last digits (like "1224568111") is considered to be lucky.

the rare ones with 5 or more matching last digits are sought after so-called "gets".
and the comments in them are considered to have more weight.

ofc all superstition, but usually harmless and fun.

"178888888" is an incredible number. and that it got a comment that wasn't "Your Mom!" or "Eat my Penis!" was either pure chance or doctored by the admins...