What makes a verb transitive or intransitive? A transitive verb requires a direct object to complete its meaning, whereas an intransitive verb does not. Resting or reclining does not require a direct object to complete its meaning. However, putting or placing requires something to be put or placed to complete its meaning. This is the difference between to lay and to lie.
I use a simple mnemonic to distinguish between the two words. To lie generally refers to someone who is resting or reclining, but to lay generally refers to something which is put or placed somewhere.
Thus, lie is to someone as lay is to something. And I know lie goes with someone because you don’t lie (tell an untruth) to something.
Take a look at the example in the cropped image. The writer uses to lay because there is a direct object (the pipe) which needs to be included in order for the verb to have any real meaning. The pipe is the something receiving the action (making it a direct object). Since you don’t lie to something, lay is the proper word choice.
These apparently small word choices may seem insignificant. But the words you choose affect how clear and effective your writing is. And better writing is always more clear and effective.