For those who may not know it stands for "Read The F....... Manual"
The reality is that it's not realistic to read and remember every detail of any programming system.
I think I wasted two days because I didn't realize that delayMicroseconds() only works up to 16384 or 5.
I had a short sketch to repeatedly send a few characters followed by a short delay as test data for a sketch on a second Uno. The delay was/is critical to detecting a start bit. I must have tried every possible combination of options for my receiving program before it occurred to me to test what was actually being sent.
It works just as I thought it would two days ago now that I have replaced delayMicroseconds with delay (and a suitably altered number).
(and the new two line editor on this new website is a PITA)