As they say, there are two rules in improv: Never say no, and never ask why. When another actor asks 'Why?' or says no to something you're suggesting, then it's very clear that they're putting the onus on you, because they're not comfortable with it themselves.
“I started with the firm conviction that when I came to the end, I wanted to be regretting the things that I had done, not the things I hadn't.”