'Hard' in the Bible

Then I examined all of my accomplishments that I had brought about by my own efforts, including the work that I had labored so hard to complete and it was all pointless, like chasing after the wind, and there was nothing to be gained on earth.

I saw all of it as the activity of God. Frankly, a human being cannot understand what happens on earth, because however hard a man works to discover it, he will not find out. Despite what he thinks he knows, he will not be able to figure it out.