What's the Most Life-Changing Beauty Tool that you've tried?

Share your pick! And don't forget to share why!
I don’t think most would consider it a tool, but cleansing oils in general made removing makeup so much easier (and efficient) that I feel I have no excuse to not remove makeup at the end of the day–when I was younger, it made a really compelling case to always remove my makeup. Now, I’m used to removing, so it seems wrong not to these days! A more tool-like item would be the T3 blow dryer, because it dries my hair so, so much faster than any blow dryer I had used previously and didn’t suck up my hair either.

-- Christine