When suspension of disbelief works - Source Code vs Knowing

I recently saw Knowing, and although the two films are not really similar in theme [or are they?], it strikes me that there is a similarity in how much suspension of disbelief is required for both of them. In contrast, however, I found this movie far more satisfying despite its obvious plot holes, and I think it must be because the characters have credible motivation. So I was willing to go along for that ride. On the other hand, in Knowing, why would time travelling telepathic aliens/God do the things they did in Knowing? I found I couldn't get past that and enjoy that movie. Or maybe it's purely subjective and I just couldn't relate to the motivations of the aliens/God.