Answer: A. It is hard for humans to evaluate events in terms of potential outcomes.
Explanation:
It is being inferred that humans find it difficult to think events in a way that enables them see the effects of these events like heaven can - line 2.
This is why they can have problems distinguishing between good and evil as inferred in the first line.
This is also why we can end up confusing enemies for friends - last line - because we do not think of the outcomes of engaging in such folly.