How are our (my) eyes able to do this?

Generally when I wear prescription contact lens I have clear vision. If I put on my prescription glasses while wearing my contacts my vision becomes total crap, like just as bad as when I'm not using any vision correction product BUT today I slipped my glasses on while wearing contacts because sometimes I forget (I don't usually wear my contacts, it's habit to reach for my glasses when I'm not wearing them) and for a few seconds my vision was crystal clear before getting super fuzzy like normal. I kept the glasses on and could see my vision struggling to focus what I was looking at, sometimes it could clear the image but usually it was just fuzzy.

How is it that I was able to see clearly at all while wearing both prescription contacts and prescription glasses at the same time?

And why can't our eyes automatically correct poor vision so people don't need glasses/contacts anymore? I'm just curious.

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