This was one of the first things I wrote about when I joined nostr. naddr1qvzqqqr4gupzqat9vaqzpxtqca87xulxjslc5gdt395gnkrfzfm2vrux4tdu37f2qy88wumn8ghj7mn0wvhxcmmv9uqq6vfk8qunwwfc8yerzdp5xy3swc0enaddr1qvzqqqr4gupzqat9vaqzpxtqca87xulxjslc5gdt395gnkrfzfm2vrux4tdu37f2qy88wumn8ghj7mn0wvhxcmmv9uqq6vfk8qunwwfc8yerzdp5xy3swc0e

Relays are a failure point in nostr because they are effectively global and only really work as intended in a delivery by default manner. I.E. since they must accept all inputs they will succumb to spam.