It’s so tempting to generalise. To stereotype.
And it’s useful.
It saves time in your dealings with strangers if you can quickly put them in a familiar box, ie: “Ah, I know this type of person, they all are dodgy/arrogant/lazy/liars.”
Generally speaking, stereotypes are accurate. That’s why they’re stereotypes.
The problem is that there are exceptions to every stereotype, and if you’re too quick to judge you risk missing that exceptional person that could be the missing ingredient for your success.
Never say “they all are…”