Should You Work Hard or Smart?

About five years ago, a senior developer I met recounted to me stories about how he aced interviews:
"I always like to tell interviewers that some people work hard, and some people work smart, but I like to work HARD AND SMART!"

It was certainly a nice sounding line that had a good ring to it, but is there such a thing as working hard and smart? Or does working hard automatically imply that you're not working as smart as you could be? Wouldn't you be working less hard if you had smarter ways of accomplishing your tasks?

You are welcome to share your opinion in comments, but here is my perspective on the matter.

It certainly depends on the definition of what is "hard" and what is "smart".

If "hard" meant working 50-hour+ weeks, then on average, people get tired after say 8 or 9 hours of continuous work on a day, and their thinking capacity diminishes as a result, resulting in less "smart" work than say at the beginning of the day. So, in that case, working "hard" affects people's ability to work "smart" and the two do not quite go hand in hand.

If "hard" meant working 35-40-hour weeks with extreme concentration, taking the rest of the days off to let the brain detangle itself and get ready for the next day, then on average, this facilitates performing work that is as "smart" as possible per people's thinking capacities. So, in that case, "hard" and "smart" do go together though people who work 60-hour weeks would not consider that "hard" enough, so it ends up just being "smart", and who doesn't like that?i

Now in the software development world, if some developers find themselves working 60-hour weeks to meet a 3-month deadline for a business project, then they certainly are working "hard", but are they working as "smart" as they could be, or should they be ditching this old unproductive framework/library they are relying on and move on to a smarter technology/programming language that offers more productivity? After all, not only will that save them from over-extending themselves, yet also allow their work to be higher quality since it will be done in the majority of hours when their thinking capacity is near its fullest on average.

Doing 12+ hour days is not necessarily bad every once in a while, especially when the developer has a sudden burst of creativity and motivation. However, if done regularly, it is important to be aware of the quality of work coming out of the long hours as sometimes it may give the illusion of accomplishment when the work is actually taking a lot longer to finish with a tired less concentrated mind, and could have been done better when rested.