Grammar Challenges

While writing and editing, I get the most frustrated with those words that no one would notice are right or wrong. Words like who and whom, that and which, us and we, can all be interchanged and most people would never know if it was grammatically correct or not, which is why they are so hard to distinguish even to a literary professional. As if that isn't enough, I'm challenged with all of the rules that come along with these words. And to keep up with all of the different rules and the exceptions to the rules is a constant annoyance. And finally, my biggest challenge is to find the motivation to correct the grammar when chances are, no one would notice the difference.