Should Happens

"I'm not bossy - I just know what you should be doing"

While doing my homework on About pages, I came across a lot of should. And when I started paying attention I noticed that should is everywhere. It's not all bad but its prevalence did spark a memory; something a hip and wise lady named Jan once mentioned:

... ... um ...

er - well it was a while ago... but it was something about abstaining from should because few good feelings ever come of it.  OK I have paraphrased poorly and it's more than likely that Jan put it to me as a question. No matter the exact wording, the message kinda stuck:
With so many less bossy options (will, would, can, could, choose to, might, even shall for starters) - what is up with all the should?

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