Most selfish 1 letter, "I" - Avoid it
Most satisfactory 2 letters, "WE" - Use it
Most poisonous 3 letters, "CRY" - Stop it
Most used 4 letters, "LOVE" - Value it
Most pleasing 5 letters, "SMILE" - Keep it
Fastest spreading 6 letters, "RUMOUR" - Ignore it
Hard working 7 letters, "SUCCESS" - Achieve it
Most invisible 8 letters, "JEALOUSY" - Distance it
Most essential 9 letters, "PRINCIPLE" - Have it
Most priceless 10 letters, "FRIENDSHIP" - Maintain it