The value of a diamond is determined by the 4Cs, but the last three, the color, clarity and the carat weight are factors of rarity. They are measures of how rare the rough material was. The cut determines how beautiful the finished product will be.
Make sure you don't confuse rarity with beauty, because you can have a rare diamond from a color and clarity standpoint, but if it isn't well cut, it won't sparkle to the best of it's ability. Long after you have forgotten the exact grade, a well cut diamond will continue to thrill and delight its wearer.
How to find a Beautiful Diamond
Although the task may seem difficult and daunting at first, you CAN find a beautiful diamond that will provide a lifetime of joy and pride of ownership. One thought that will keep everything in perspective as you shop is to remember why we value diamonds in the first place. People the world over wear and cherish diamonds as everlasting objects of beauty that symbolize their love and commitment.
So when you shop for a diamond, spend some time really looking at each stone you're considering, get it out from under the jewelry store lights, and look for the one that dazzles, that dances, that grabs your eye and won't let go. They may all look the same to you at first, but stay with it and soon you'll be amazed at the differences you'll begin to see, even between stones with similar grades.