this is endless endurance: http://www.cardgamedb.com/forums/uploads/1281656500/med_gallery_6_303455.jpg

let's say I have 3 endless endurance in my discard pile and I win a military challenge by 4 strg. do I get all my cards back or only one?

Remember that you trigger ech card individually, and return each one to your hand individually.

Is there any particular reason you might think you couldn't trigger the Response on each individual card?

I thought winning a challenge might be considered to be the ''cost'' to trigger the effect

Robby Stark said:

It is, technically, but that's why on certain event cards that trigger off of the occurence have that handy phrase "once per challenge," or "once per phase."

If it does not have the stipulation, and/or you're not trying to trigger more than one of the same response if it does, then you are allowed to do it as many times as you have the responses. This is the same reason you can trigger No Quarter and Die by The Sword off the same MIL challenge, as long as you have both a unique character and a war crest character in that challenge.

stormwolf27 said:

Winning the challenge is a play restriction, not a cost - technically or otherwise. Costs are the resources you must pay in order to initate the specific effect. Play restrictions are the conditions that control when and how often you may initiate an effect. 

If winning the challenge were a cost, you could only use one "after you win a challenge" Response because you cannot pay for multiple effects with the same resources (e.g., you cannot pay for two different characters with the same gold token, or pay for two different 'Lannister Pays His Debts' with the same knelt Lanni character). But a single condition can be part of satisfying the play restrictions for many different effects. Said another way, "after you win a challenge" is going to be true from the time the challenge is resolved to the time the action window closes, so things that can only be played "after you win a challenge" can be played during that time -- provided you have the resources to do so.

The fact that winning the same challenge can be part of meeting the play restrictions on two separate effects - like No Quarter and Die By the Sword - has nothing to do with the absence of "once per challenge" limits allowing you to pay the cost of multiple effects. It has to do with the fact the two effects have similar play restrictions, one of which is winning a challenge.