Count no man happy until the very end.
Consider the case of Michael Jackson. When he was 25, he was on top of the world. By the time he passed away, most people still acknowledged his amazing talent, but also felt sorry for him. Who would have wanted to trade lives with Michael Jackson at that point? Not any reasonable person. Life is long if you know how to make the most of it, and short if you don’t — but no matter the length of the book, your life will only become a complete story when it is over. You may have a lot of good times here and there, or you may be miserable more often than not, but as the Bard said, “All’s well that ends well.”
The Bard forgot the second half: Nothing's well that does not end well. You must consider every decision in light of how it will affect your happiness during your last lucid moments on Earth. Consider the example of a father who abuses and rejects his children. His unkindness may satisfy his pride in the short run — and he will always be able to find people to back him up in his obstinance (every bully does) — but will such a course make him happy at the end of this life, or (potentially) in the life to come? Obviously, the answer is “no.”
Consider those who enjoy humiliating others, and who refuse to accept responsibility for the consequences of their own words and actions. Such people may enjoy moments of laughter and “happiness” at someone else’s expense, but misery is the inevitable net result in the final stretch of life.
The worst part is that the nature of fatal character flaws prevents us from accurately pinpointing the source of our misery. We each regard our favorite sin as a given, or as a special privilege. As a result, we rarely question ourselves; we only question the reactions we receive from others. Over time, our bad tendencies become total commitments, until we are genuinely incapable of acknowledging our wrongdoing for what it is. The point is this: You must choose your habits wisely, because your habits are your fate. Many otherwise good people are undone in the final stretch of life by a single, overpowering vice that outshines all of their virtues.
Unkindness is perhaps the best example of such a vice.
It does not matter how “good” or “successful” you are; if you are unkind, the sum of your life will be multiplied by zero.