I will allow someone else to explain it to you.
(I admit, I relish in a guilty pleasure here: This is redolent of Ultimate Finality #5 or Final Destination No. 7.)
"It goes from bad to worse, and then to worst."
Since, these questions are about learning a language, let me say that "worst" is the superlative form, so if something is truly the "worst," then it of the greatest or highest extreme of something that is unpleasant or bad in quality.
She was a bad player, but her sister was the worst player on team. (Which means she was
to the highest extreme of playing poorly, and the only player at that level.)
He was a bad president, but Johnson was worse; yet, Nixon was the worst.
I hope that helps.