So I am playing Massing at Osgilath and my fellowship is in a rather good shape. Ten Dwarves and one Ithilien Ranger try to cross the Anduin at stage 3B. The Ranger sacrifices gimself give the Dwarves some time to cross the Anduin. Everything is fine, but then one fatal mistake ruins the game immediatly:

Golden rule: think first, act afterwards! Should have followed that principle when I decided to commit Longbeard Elder to the quest without taking his special ability into consideration. I start with 10 WP against 2 threat, but I get "Captured Watchtower" as encounter. The Elder's response triggers and I have to (do I have to choose to trigger the response?) place a progress token on 3B which finishes the third stage and brings me right to the fourth stage before the quest phase resolution with all the nice little side effects of having crosssed the Anduin. Like adding the Witch King to the staging area. Like turning the two Captured Watchtowers in 8 points of threat. And suddenly it is 6 WP vs 15 threat, my threat level skyrocks to 44, and the game is over, as I am not able to take out the Witch King with my few remaining Dwarves and all Gandalf's being used.

Responses are optional, forced effects are mandatory. 

If you 'have to' you are not 'choosing'.

Wouldn´t make a difference if you trigger the response or not.

The card reads: Progress tokens from card effects cannot be placed on this quest card or the active location 

So the Elder cannot put a token on it. You would have been fine.

Well, eh, I guess that guy hypnotized me with his big yellow lantern to make me forget that he couldn't use his special ability…

"I can always place progress tokens on quest cards…"

"I can always place progress tokens on quest cards…"

"I can always place progress tokens on quest cards…"

"I can always place progress tokens on quest cards…"

"I can always place progress tokens on quest cards…"

"I can always place progress tokens on quest cards…"

"I can always place progress tokens on quest cards…"