I just remembered something about a friend from an old job. His father (or grandfather I think) was ill, quite badly ill. He recovered and his grandmother said it must have been because she and her friends prayed for him to recover.
Assuming there is a big plan laid out for all of us, this would mean praying to God would have persuaded Him to reconsider someone's destiny, and the destinies of all those affected by it.
What's more, what if the guy had actually died? Would that have been "part of God's plan"? So why would He be willing to delay the death of some people and not others when it's all part of His plan? I guess this goes for hypothetical situations where there is a plan and where there isn't a plan. If there isn't a plan, what goes wrong when praying for someone's good health doesn't work?
You could say that, through seeing how many people cared and prayed for the ill fellow, God saw how concerned people were about him and allowed him to recover, but if God is omnipresent and omnipotent surely he should have known already?
Allowing him to recover after seeing how many people would be upset by the person's passing? Everybody dies eventually, why would God simply delay the inevitable?
There's one thing about factory work...it gives you time to think crazy questions like this.