We tend to believe that bad Karmas will not get accumulated on account things done put of ignorance about the consequences. if we do things well in matters which are within our cognition..After all things and acts handled consciously shape our attitude and habits.. And we can trust in the mercy of the God too in matters which are beyond our control..
Of course these are theories, reflected in philosophy.. but there are terse philosophies like Sankhya and Nyaya which would state that if you eat a lot of salt you will have to drink water too..no prayer, no entreaties can reduce the severity>
The world and life in general is full of uncertainties,, so we have to go by trust .. God does not get any benefit by our prayers..