"Go, eat your food with gladness, and drink your wine with a joyful heart, for it is now that God favors what you do. Always be clothed in white, and always anoint your head with oil. Enjoy life with your wife, whom you love, all the days of this meaningless life that God has given you under the sun - all your meaningless days. For this is your lot in life and in your toilsome labor under the sun. Whatever your hand finds to do, do it with all your might, for in the grave, where you are going, there is neither working nor planning nor knowledge nor wisdom." NIV translation
This passage speaks of the rich and the fact that they can enjoy the things of this life but, at the end of their days, they still go to the grave. If you believe that this world is all that there is, then, you will work at it to get the most out of it. There are those who spend their entire life trying to get more so that they can stay ahead of others and be considered "successful".
"I have seen something else under the sun: The race is not to the swift or the battle to the strong, nor does food come to the wise or wealth to the brilliant or favor to the learned; but time and chance happen to them all." NIV translation
Next, Solomon tells us of those who put their hope in luck or chance.
In our world today it seems like everywhere you look there is a lottery or gambling and people with the "hope" of striking it rich. Many times they do win but it is only temporary as they tend to spend it foolishly and it goes quickly.
"Moreover, no man knows when his hour will come: As fish are caught in a cruel net, or birds are taken in a snare, so men are trapped by evil times that fall unexpectedly upon them." NIV translation
When you start thinking that life is just like a giant game of chance, then, you get to the point of living like today is your last day. That may sound good and it actually could be if you served Christ like He was coming back today. But, that is not what Solomon is speaking about. He is talking about people without Christ living it up like there is no tomorrow and no eternity to answer for our actions.