Of all the 4Cs, Cut is considered to be the most important. After all, it is the cut that gives the diamond its brilliance, its fire, and its scintillation:
An excellent cut can breathing life into the diamond; while a poorly cut can make the diamond dull and lifeless. Excellent cut doesn't simply mean the shape of the diamond. It entails crafting the perfect symmetry, the polishing, the angles and the proportions of each physical aspect of the diamond.
Most diamonds are cut round with 58 facets (as this number is deemed to be the ideal number that maximize light reflection). So, what constitute a well cut diamond? To truly understand this would require lots of mathematical formulas and illustration of physic principles that would make your head spin. For the ease of understanding, the simplified theory is this - a good cut is a cut that results in maximum light reflecting back to the eye, while a bad cut is a cut that results in less light reflecting back to the eye.