There are so many times when I have had to explain that these are actually different words with different meanings and different morphologies.
Obviously, there is a shared etymology here from Middle English leyen and Old English lecgan but, in the eight hundred years since the thirteenth century, this single root has diverged. To lay is transitive and requires an object to have been put down; to lie is intransitive and has no need for an object.
And, it goes without saying that the homophonous (and also intransitive) verb to lie meaning to deceive and dissemble is from a different root altogether: the Old English lēogan. Phonologically equivalent but etymologically and semantically totally distinct.
Who says the English language is easy?