i'll get that one wrong, sometimes, because the logic is blurry. it's not always clear what the right choice is, and sometimes it doesn't make sense.
i need to call for a re-evaluation of the english language to root it in proper axiomatic principles, to allow it to be deduced fully from first principles, so you don't have to memorize stupid rules and can figure it out on the fly, instead.
so, i reject the conventions around it's v its and use my own conventions, instead. it's should be both possessive and a contraction; its should only be plural, which is almost incoherent. so, i almost always use it's and will tell you your rules need to be reformed when you challenge me on it. and, i may have to come up with something similar for effect v affect and stick with it.