Jake needs to climb a tall, steep ladder 50 feet to get to the top of the roof. Below him is his employee, Donna, who is holding the ladder in place. Without Donna holding the ladder, the ladder will slip, and Jake - well, let's just say that he's not going to be too happy hitting the ground from 50 feet up. Now, Jake is almost at the top of the ladder, and Donna calls up to him, letting him know that he has not given her an answer on her request for more money. Jake hollers back that now is not the time to talk about it, and we can talk about it later. To which Donna replies, 'If we do not talk about it now, I am quitting, and you can get someone else to hold the ladder for you!' Jake, after taking all of about 10 seconds to think about how far down the ground is, grants Donna the raise she asked for, and the ladder would stay where it is.
Now, in the case of Jake and Donna, Donna was not _ because Jake could eventually find someone else to hold the ladder, but he could not do it at the time he needed it.