If you have to pick between working hard -OR- working smart, work hard.
Of course, you don't have to pick. But our culture has an idealized working smart as an alternative to working hard (which is a stupid), so a lot of people believe you have to choose.
Obviously, working smart is better than working dumb.
Nobody ever sets out to work dumb; everyone thinks they're working smart.
So when people say they're working smart, it's usually just an excuse to justify why they don't work hard.
The culture of celebrating "working smart" is the same culture of looking for shortcuts to get rich quick, cutting corners with shoddy work, and finding "hacks". It's the culture of being a C++ expert in just 21 days and creating a tech startup just to get acquired in 4 months. It's the culture of "one simple trick" that will make you lose your belly fat, have more sex, or earn $2,000 per week from home in your underpants
You should definitely work smart.
But most everyone believes they already are working smart. And a lot of us are definitely working dumb. So how can you tell if you're deluded? You probably can't.
So if you tell yourself you're working smarter not harder, but you're not a good judge of smartness, then you're probably just working dumb and lazy.
The good news is you can control working hard. Then at least you can be that really rich, successful dumb person that everyone thinks: "That guy is really dumb. If he can make it, anybody can!".
There's a place for working smart. It's just not in place of working hard.