Because Sid has always been there to solve all their problems, even before they screamed for help! DD has high expectations from Sid, almost to the point of taking him for granted! So, when he does things like this, which isn't expected of him, she automatically gets mad! In a way, you cannot blame her, as Sid hasn't told her anything for her to think or worry. He hasn't told Roshini anything.. none of them has in inkling as to whats going on! All DD is basing it on, what she is seeing/observing. According to Sid, he is doing the right thing. and according to DD, she is understanding it correct. But, as usual, there is a gap in communication.. which leads to so many unavoidable things! sigh.