Achievement-oriented people often experience a weird kind of emptiness shortly after they reach their goals. As Tom Landry, former head coach of the Dallas Cowboys, once put it:
"Even after you've just won the Super Bowl -- especially after you've just won the Super Bowl -- there's always next year. If "Winning isn't everything; it's the only thing," then "the only thing" is nothing -- emptiness, the nightmare of life without ultimate meaning."
I have never won the Super Bowl, but one of the small victories in my life was when I finished my second university degree. I was already working full time by then, so I had to sacrifice many evenings, weekends and most of my vacations for studying. After my final exam, I was satisfied and happy - for an hour or two. Then suddenly a sense of complete emptiness overwhelmed me. The goal which had fulfilled me before, it suddenly was gone. It took me several days of exploring new objectives, some at work, some regarding my personal life, until that feeling was gone again.
Still, just setting the next goal is only going circumvent the problem momentarily. On the long term it's a mistake to define the meaning of life by such one-dimensional purposes that will be accomplished sooner or later.