Lot's of elements here.

It can be said that it has been abused and exploited which is why in the game Skyrim, they have been in a severe decline since multiple sanctuaries had been destroyed. The same fear that took down the Morog Tong at the height of their power has also affected the Black Hand. And the Morog Tong actually has clearly laid out guiding rules as checks and balances to try to ensure that it always has political allies. e.g.: All of it's contracts are intended to keep one House from getting to powerful, with the intent of maintaining an intended balance in Morrowind.

The Brotherhood is more religious and fanatical than the Morog Tong but that isn't to say the Black Hand has no checks and balances. Also in Skyrim, we see that Aventus has been "trying to summon" the Brotherhood. Which means that simply performing the ritual is no guarantee of securing a contract. There seems to be a spiritual/emotional elements that the Night Mother can either perceive or requires before a successful contact is established. So, there are requirements to be fulfilled beyond simply conducting the ritual but they are poorly defined.

edit: canceling the contract by killing the assassin is a good point.

Let's not forget: in Oblivion at least, summoning the Dark Brotherhood is illegal - that's how one of the NPCs in the prison ended up there. It's reasonable to assume that other major governments had similar laws, so their lawmakers wouldn't get targeted. So if you keep summoning them, sooner or later the guards will notice and arrest you.

Also, the more important/powerful someone is the more likely they are to have bodyguards in their employ, and people with a lot of personal power in the non-political sense (exceptional fighter, powerful mage) are probably hard to take down. The Brotherhood doesn't have an unlimited number of assassins, getting one that is qualified to do the job into place may be very time consuming for targeting (EX: ) the Emperor - witness Skyrim.

Tyrobag wrote: »

The more high profile a person is, the more expensive it is to take out a contract on them. We know that killing an emperor (even in a time that the empire's power has waned considerably) is prohibitively expensive, well out of the range of the average person.

The dark brotherhood also does not take conflicting contracts, which would prevent such "vicious cycles".

We've also been given reason to believe that if an assassination is foiled, and the assassin killed (for low profile contracts at least) then a second attempt will not be made (unless they are paid again). This is of course unconfirmed, but the events in skyrim (assassin sent after the Dragonborn, without a second attempt for the same crime) seem to imply this conclusion.

Not to mention that the Black Sacrament is somewhat unpleasant, and extremely suspicious to acquire the materials for. That would deter many people.

From a player perspective it makes sense gameplay wise that after a failed attempt on your life they would stop. I can imagine it being very annoying to have Assassins at your heels through out the game as you try to explore and see the world.

But from a business perspective with a contract involved. Its important to keep sending assassins until the contract is fulfilled. Its very bad business for an assassin organization to not hit their mark. If other potential clients get wind of your organization failing to accomplish what it promised to do after taking money from a client. Theyre going to look elsewhere for their needs. That trust and expected reliability will be lost.

Korah_Eaglecry wrote: »

But from a business perspective with a contract involved. Its important to keep sending assassins until the contract is fulfilled. Its very bad business for an assassin organization to not hit their mark. If other potential clients get wind of your organization failing to accomplish what it promised to do after taking money from a client. They're going to look elsewhere for their needs. That trust and expected reliability will be lost.

To start with, it is unlikely that they would fail most of the time. Also, if they can't kill somebody it would be even worse business practice to keep sending assassins to their deaths (at least not without proper compensation from the client). When you hire the Dark Brotherhood you are paying for a single soul to be sent to Sithis. If the assassin is killed, then one life is lost, and one life was paid for.