There are some SI clarity diamonds that are not eye clean and should only be used for earrings or pendants, not for engagement rings. I1, I2 and I3 are commercial grade diamonds and should be avoided except perhaps for I1 in earrings. Many people unwittingly buy I1 and I2 stones in uncertified stones, but if you shop carefully you can buy an SI1 stone for a great price and not worry about clarity. Therefore, target SI1 or VS2 as the best clarity values with outstanding beauty. A diamond is the hardest thing in the world, but not the toughest.
Diamonds can get abrasions or even chipped through normal wear and tear.
Be careful any time that diamonds might come in contact with another diamond. Diamonds are valuable objects and should not be abused.