In another 30 years, I will perfect a time machine. The old me came back in time, and planted that dental floss there. Unfortunately, I could not tell my younger self why, as this would cause a temporal paradox.

While this would not end the universe or anything, temporal paradox apparently causes a nasty rash, and the future world is in the midst of a horrible hyrdocortisone shortage, and it seems my elder self really hates being itchy.