It's not that hard to get it right!

Sigh. The four most lucrative times of the year for me are the annual film festivals--Cannes, Toronto, Berlin, and the American Film Market, which is due to open in little over a week. I read between 30 and 100 movie scripts in the weeks running up to the markets, and sometimes I have to subcontract the work in order to get it all done.
I've gotten used to certain errors I see over and over and over again in scripts ("Vile" of cocaine"; "His breaks failed"), but I'm starting to get a little nuts about the mistakes my subcontractors routinely make.
The most common error is mistaking ITS and IT'S.  Seriously.  It is not that hard to keep them straight. Ditto for WHOSE and WHO'S. My contractors are smart people, good writers, educated. But somewhere along the way, they just missed a couple of things.
My best friend mocks me when I go off on this stuff and calls me a "word snoot."
And it's not like I don't have weaknesses.  I can't spell graffiti to save my life. I always want to put in one F and two Ts.  I'm not really clear on THAT and WHICH.
But I know IT'S and ITS.
I actually blame Spellcheck. Have you ever noticed that Spellcheck will challenge your every use of ITS and IT'S? If you're not rock solid on the rule, it would be VERY easy to get it wrong. 
I try to remember that as I go through the work I get back.
I fear I am becoming the grammar equivalent of the cranky old person who tells kids to get off his lawn.