The sluggard is always wanting and never getting. His life is a series of desires and cravings for everything under the sun. He craves and speaks of all the things he wants - but does nothing to actually obtain them. If someone gives them to him he is happy for a moment or two. That happiness is soon replaced with another craving, though, and he returns to his world of constantly wanting something else. In all his wanting though, he never lifts himself up to the level of work and labor. These things would open his life up to actually seeing things happen. He is lazy and undisciplined and therefore he never attains to things. The proverb tells us that he gets nothing. His hands are always empty - first they are empty of work and labor - and in the end they are empty of any real productivity and products. He is a sad soul - doubly empty.
The soul of the diligent man is fat. He works hard and labors diligently at the things he wants. He allows desire to prod him to work and labor. Thus his desires and wants become more than just a craving that taunts him. He uses those desires to spur him to action - first action of the mind - and then action of life. He works hard - and at the end of the day has something to show for it. If not his actual goals - he has the satisfaction that he is one day closer to seeing them realized. Along the way his soul gets fatter. His mind is filled with thought of how to do things better, quicker, with greater quality and skill. Along the way his will is set to do what is before him. Along the way his emotions are kept in check - not dominating his life with unmet cravings and the whirlwhind of emotions they bring - but with excitment about what is coming as his work yields true rewards. Even before he gets what he is working for - his soul remains fat with the good things that come from hard work and industry.
One craves and is wracked by the unmet cries of his cravings. He is starving to death physically, emotionally, and mentally as he has nothing to show for doing nothing. The other is working toward something good - and all along the way good comes to him. It is far better to be working toward something than to be only craving what you will never get.