Why do my pages keep falling in and out of Google's index?

• We seem to be having a problem with pages being indexed by Google and then, for some reason, disappear only to show up again when we resubmit them. Do you have any idea what might be causing these pages to keep falling out of Google's index?

Answer:

It sounds like you're teetering on the edge of indexing perhaps due to quality issues. This is something that Gary Illyes of Google addressed in a tweet a while ago...

as we fine new URLs, the page may fall out the index, but then you breathe new life into it temporarily by submitting to the index manually.

— Gary 鯨理／경리 Illyes (@methode) July 28, 2021

John Mueller addressed this issue as well in a recent tweet saying,

If you're teetering on the edge of indexing, there's always fluctuation. It basically means you need to convince Google that it's worthwhile to index more.

So, what does it take to convince Google that your pages are worthy? ... in the tweeted words of Googlemeister John Mueller,

Awesomeness.
Lots of awesomeness.
All kinds of awesomeness.
And add more awesomeness.

— John (@JohnMu) November 8, 2021