Board Thread:Lore Discussion/@comment-92.251.228.132-20141108020915/@comment-5424581-20150924134411

Draevan13 wrote: 177.34.181.193 wrote: They are also a guild of assassins that does minor contracts like every other. The difference is that they don't fail. The Dark Brotherhood has failed before: 3 seperate attempts on Adamus Phillida failed, the attempt on the Nerevarine in Tribunal failed, the attempt on Queen Barenziah failed, and Lachance failed to kill Telaendril then ended up recruiting her.

They're good, but not infallible. And if you count the random encounter in Skyrim it could be many more depending on how many times they came after you.