If You Need Some Practice Writing (Atomic) Zettels
I have recently been reading through notable "commencement addresses" by famous people, some of whom I recognize and admire, such as John Brodsky, Kurt Vonnegut, Bill Watterson, Neil Gaiman and Richard Feynman (and many others). It struck me that this material would be an excellent source for people new to the Zettelkasten world, who might like to practice writing zettels from short and interesting (but not too demanding) essays. It might even prove to be the source of some zettels that you want to include in your own ZK 
See: https://www.brainpickings.org/2014/05/20/the-best-commencement-addresses-of-all-time/
My apologies that these seem to be US-centric, likely due to the predilections of the person preparing the compilation. If there are other sources of which you are aware, from other countries or cultures, please post a (some) link(s) to them.
Howdy, Stranger!