Time travel.

When I was young I used to sit in my room and say to myself: 'If time travel is real, I'll come back and put a Mars bar under my pillow.'

This has never yet happened.

It nearly happened the other day when I put a Cadbury's Caramel on the bed, sat down and it reappeared behind me, but it was in fact gravity and not a future version of myself travelling across time and space in order to furnish me with confectionery that will likely not exist by the time that such an endeavour proves possible.