It is wrong to post movie spoilers publicly.
Jeff is participating in an online forum about a TV show he just finished watching.
Jeff wants to know how other participants feel about the ending of the show.
Jeff posts a large and very visible SPOILER title at the beginning of his post to warn others.
Jeff discusses the ending of the show on the forum, revealing it to all those who read the thread.
Participants who have not watched the finale yet skip Jeff's comments when they see the title and can enjoy the show's finale.
Participants who have not watched the finale yet are disappointed by the spoiler, which ruins their experience of the last episode.