Thank you! I read further on that Fake Buddha quotes site (motto: "I Can't Believe It's Not Buddha!"), and learnt a lot from the comments and discussions, e.g. on this page[0] - like that some Buddha quotes I've 'known' for decades are just very bad mistranslations. Very grateful.

[0] https://fakebuddhaquotes.com/we-are-what-we-think-all-that-w...

Sorry, I have an annoying habit of chasing up fake-looking quotes. That one sounds like a 20th C American, and....indeed seems to be - apparently it's from a Jack Kornfield book, he was paraphrasing Don Juan in the Castaneda books, themselves fakes. Interesting discussion here:[0]

Here's (I believe) an actual Buddha quote on the topic, which I've always liked/thought scary:

This existence of ours is as transient as autumn clouds. To watch the birth and death of beings is like looking at the movements of a dance. A lifetime is like a flash of lightning in the sky, rushing by, like a torrent down a steep mountain.

They sure could write in 600BC huh.

[0] https://fakebuddhaquotes.com/the-trouble-is-you-think-you-ha...