Why is pathetic fallacy effective?
It's effective because it reflects the character(s) mood and emotions, subtly.
Pathetic fallacy is the use of inanimate objects projecting the undertone and/or feelings and emotions at that current time. The most popular one would be the use of the weather.
You know when that really nice character dies, and it starts raining? Or when lightning starts and thunder sounds, right before a fight? These are very popular, almost 'cliche' uses of pathetic fallacy. Of course, there are subtler ways to do it. And in my opinion, the subtler, the better.
Hope this helps :)