"Not Bad" and "Quite Good" - these phrases in British English are particularly complex.
Take this situation.
Alice at a bar. Conversing with her girl friends. Checking out potential dates.
"She's not bad." All her English friends understands she just rated someone 7 or 8 out of 10. Her Spanish friend, Maria, thinks she just rated someone 4 or 5 / 10.
Maria asks "What about that girl in green?"
"She's.... quite good." [Note the very slight intonations or pause or speed of phrasing on the 'quite' will be immediately parsed by her English friends.]
Maria thinks green girl scored 7 /10. But, Alice scored her 5 / 10.
"What do you think of my dance moves? --- Errrr. Quite good!" English people can sound perfectly pleasant while telling all their English friends what they are really thinking.
The same situation applies to business. If your work or someone else is described by your boss as "Quite Good" it was average or possibly even slightly below. If you boss described it as "Not Bad", "Not Bad at all", then it was good and above average piece of work.
If you'd like to feel inspired by life lessons try: Ursula K Le Guin on literature as an operating manual for life; Neil Gaiman on making wonderful, fabulous, brilliant mistakes; or Nassim Taleb's commencement address; or JK Rowling on the benefits of failure. Or Matt Haig's life lessons.