Having an imagination is one of the best things in the world, I think. I am very easily pleased, because I have an imagination. Give me a cardboard box and I can amuse myself for hours...Yes this is coming from a 22 year old! As long as you have an imagination you can do anything, as John Muir says above. If you want to go to the moon, then go; if you want to be a rock star then sing; anything and everything is possible if you imagine it.
Some people may think it childish to imagine you can fly to Mars or beyond in a cardboard box, but in the long run I think its those who have very little imagination, and take things at face value who are the childish ones.
On family a family vacation many years ago, we visit an old Castle ruin in Shropshire UK. As we walked up a flight of 500/600 year old stairs, I could hear the hustle and bustle of the Castle occupants as they went about their daily business. Footsteps going up and down, running errands, or just going places. Then as we stood over what used to be the Great Hall, which is now just a shell of the outer walls, I could see the huge table down the centre, the roaring fire at the end of the room with people milling about drinking from their tankards or goblets. There were women in their float dresses with flowers in their hair, men sitting at the table eating the great chunks of bread and meat. I could feel the warmth of the braziers on the wall, giving out the flicker light which dances on the walls. The musicians in the corner playing a lively, cheery song, keeping the guests entertained. It was just wonderful. If I could choose to live in one period of history, it would be in the Medieval times, in a castle, so to visit one, and have the imagination to actually BE there, even for just a few minutes, is something that I'll never forget.
I hope that you all have at least some imagination to achieve the unachievable!