The flavor text is a reference to the joke: "Why is six afraid of seven?" "Because seven eight nine."
Wowhead has the drop rate of the The 5 Ring at 3% from [Tiny Titanium Lockbox], and the TTL itself at 0.2% from the [Bag]. This suggests you have a 0.006% chance of getting The 5 Ring on any particular day. You would have to do 11552 daily fishing quests to have a 50% chance of getting the ring. That's over 31 years.