If anyone could be nicknamed the Eeyore of the Old Testament, it would be King Solomon in the book of Ecclesiastes. Take a look at some of the things he said in just the first chapter: "Vanity of vanities, all is vanity" (v. 2). "What profit has a man from all his labor in which he toils under the sun?" (v. 3). "All things are full of labor; man cannot express it. The eye is not satisfied with seeing, nor the ear filled with hearing" (v. 8). "That which has been is what will be, that which is done is what will be done, and there is nothing new under the sun" (v. 9).
To finish it off, he called life a "burdensome task God has given to the sons of man" (v. 13) and said, "I have seen all the works that are done under the sun; and indeed, all is vanity and grasping for the wind" (v. 14). That's the rest of the book summed up: everything under the sun, every experience that you try, is ultimately vain and empty. Living life only on the horizontal plane is tedious, monotonous, and predictable.
Now, there is truth to this: you can partake in all the pleasures life has to offer and you still won't find satisfaction. But Solomon was missing something that Paul the apostle addressed in Romans 8. Paul wrote that "the creation was subjected to futility, not willingly, but because of Him who subjected it in hope" (v. 20).
In other words, yes, life is empty, but God designed it to be empty on purpose. He put a hole in your soul that can't be filled by anything on the horizontal level. It has to be filled by something on the vertical, or spiritual, plane. As C.S. Lewis wrote, "If I find in myself a desire which no experience in this world can satisfy, the most probable explanation is that I was made for another world."
Later on in Ecclesiastes, Solomon started to look upward and consider the Lord in all of this (for example, see Ecclesiastes 3:14-15, 17). Only then was he able to make sense of the world. In the same way, when you add God to the equation of your life, it tips the scales. Your uplook will change your outlook. You will move from cynicism to optimism. Apart from God, life on earth is just a bad joke; there's really no point to it. But with God, life makes a great deal of sense.
In the end, Solomon wrote, "Let us hear the conclusion of the whole matter: Fear God and keep His commandments, for this is man's all. For God will bring every work into judgment, including every secret thing, whether good or evil" (Ecclesiastes 12:13-14). No longer was he bemoaning the vanity of life.
If ever there was an Old Testament book that anticipated the New Testament, it's Ecclesiastes. Life under the sun—on the horizontal, without God—is flat, tasteless, insipid, boring, and empty. But life under the Son—the Son of God and Son of Man, Jesus Christ—is full of wonder and overflowing with meaning. And it's so much better that way.