Because Everybody Needs A Life Goal:

Drifting lazily inside an aluminum cocoon, miles above ground and air in radiation and vacuum, you work. Bathed in flourescence, breathing recycled air and drinking recycled water, you share the cramped space with five others. The work you do is largely thankless- the public eye is focused, justifiably so, on more pressing matters on the planet. You don't mind, though; you're not doing it for the fame. You're doing it for many other reasons- adventure, knowledge, the experience... and of course, the view. Below you, the gentle curve of Earth is resplendent with the blues and greens of the South Pacific, soft white clouds casting a shadow on the water. Twenty-five minutes ago, you witnessed a brilliant sunrise illuminate the station you call your home, brighter than you ever thought possible. A little over an hour from now, you could take a spot on the other side and watch the sun disappear behind the planet once more. It is just another example of the concept of relative perspective, and it leaves you in awe as to the grandeur and scale. The experiments on the station build a solid foundation for humanity's understanding of space- an understanding that is crucial toward future exploration. However, many can be converted to everyday applications, improving life on Earth. Alloys created in microgravity allow new materials, and new properties for existing materials. Plants, animals and minerals grown and raised without a strong downward force help identify and highlight the stark differences that need to be adjusted for. Working in close concert with these five others, you blaze a trail for humanity's future.

As is fitting for such an extraordinary experience, only hard work and diligence has enabled your stay here. Sacrifice, focus, and patience have enabled you to learn the skills, and time spent serving your country has provided you with the experience necessary to achieve such an esteemed position. Looking back, you're glad you stuck to your plans, and never lost heart. Encouraging words would have been helpful, though, for all of the difficult times, especially at the beginning, and during your stay in the military. If you could go back in time and say something to yourself, it would probably go something like this:

"It is worth it. For every ounce of strength and will invested, for all of the time spent planning and worrying, for the sacrifices made; it will be returned tenfold in wonderment and satisfaction. Every moment spent is novel, an experience worthy of note unto itself. Satisfaction resides in the knowledge that you are on the forefront of human development, setting an example and allowing others to learn from your work. Always keep this in mind. Remember: perspective is key. When the weight of the world and its trifles bear down on your shoulders, never lose sight of your ultimate goal. It is purpose that keeps us driven, and drive that achieves our purpose."

Or, in other words:

"Just don't forget that all of this work and petty bullshit now means that you'll be able to go into space later."