Hard work is... well it's hard, but only working smart can guarantee you can maintain your energy levels, sanity and control over your life.
Hard work is not only not enough, but is the wrong way to go. Your energy input is very high, your focus is high, but you quickly drain yourself, you lose the big picture, and you also lose your life in the process... and in the end you become miserable.
And I'm saying this, cause I live among people for whom life is work, who can't even enjoy themselves without working. In fact they become sick when they can't work! The mentality of hard work is that bad!
And in the end of the day work is supposed to bring you money or resources to live, it should make you happy if possible, and if you can make others happy with your work, you're definitely doing the right thing.
This can be done by observing nature, which flows freely, which doesn't push, which adjusts, and which takes the road of no struggle to achieve its goals, and in the end has a lot of resources to spare. Now that's being really smart!
In fact I have nothing against hard work. The problem is that some take hard work to fatigue, and that usually happens when you're not smart, or have no prep. This of course, if we see hard work not only as physical or office work, there are people who work hard, but at the same time do it for a short time.
Cheers!