It's about someone obsessed with their own life. They are narcissistic. They cause their own pain and suffering because they are the only ones that exist in their perspective. Once the man reveals that all people hurt themselves through their own actions and thoughts, everyone lies down on the ground. The people lay on the ground because they realize that if they want to stop their self-inflicted pain, they can't do anything. Because if they did anything, the repercussions of their actions could hurt themselves. They do not want to hurt themselves, and no one else can hurt them because no one else is doing anything.
Another interesting point is that they brought the revelation on to themselves. Proving the original man's point exactly. They wanted to know the answer even though they saw the consequences in front of them. This also showcases their selfishness.

I came to my conclusion through a few different sources.
The original narcissistic man comes from Radiohead revealing that they are singing about a narcissistic man.

The "you-do-it-to-yourself" view on life comes directly from the lyrics.

Parts of my interpretation are based on multiple other interpretations on the internet.

Finally, my last source is the tv show Neon Genesis Evangelion and the movie End of Evangelion. The show and movie showcase a protagonist who tries to do as little as possible. The protagonist also frequently tries to stay uninvolved as much as possible. That is where the "people-who-do-nothing-can't-harm-themselves" bit comes in. The 'holy cow' bit is probably a reference to Hinduism, which holds the belief that pain is self inflicted. The people may also be laying on the ground to achieve Moksha. An understanding of everything and perfect peace between the individual and collective soul. Evangelion actually incorporates many of these beliefs.

While I do not necessarily agree with these views, I can see where they come from and why it is what it is.

Thank you.