Fewer: If you can count it, use ‘fewer’
eg: We have fewer cakes than we need.
Less: If you can’t count it, use ‘less’
eg: I have less respect for you now.
Yes. This one is a big pet peeve of mine. Less also applies to collective nouns. So, less money but fewer dollars. Less weight but fewer kilograms.
I’m glad you posted it so I can do it fewer often.