Um, so English is difficult! We have all these freakin' idioms (metaphorical phrases), homonyms (words that sound the same but mean different things or are spelled differently), acronyms (abbreviations that create words spelled by using the first letter from each word in it) and more. Almost daily I see the improper use of these common words:
to, two, too
their, they're, there
a part, apart
But there are more difficult ones (and words that sound really similar):
mete, meet, meat
and this is just the beginning... sheesh!