Description I took an arrow in the knee
Beware of flying arrows!
If one hits you in the knee, nothing will be the same as before...
The original sentence I used to be an adventurer like you, then I took an arrow in the knee comes from a melancholic NPC soldier in the video game The Elder Scrolls V: Skyrim.
In the meantime, it has developed into a so-called Snowclone ("phrase template") and spread on the internet: you can find this sentence everywhere in a modified form, where the first part is interchangeable, and the second part always remains the same ("I used to xxx, then I took an arrow in the knee.")
If you have played this game or just surf a lot on the net and are interested in current internet phenomena, then you should not miss the I took an arrow in the knee shirt.