I don't know why,either.
Extra question,does YET have to be placed there?
I mean,could i say"i have to do it yet"or "Yet i have to do it"?
(Suppose YET is the right one)
I have already done it. (I did it sooner than expected.)
I have yet to do it. (I haven't gotten around to it as of this time.)
You could also say:
I haven't done it yet.
good to know
I have yet to do it.
now i got it :)