What is possible and what is not possible.
It can happen. There is a possibility of magic on the page. There is a chance that you will see unicorns and there will be faeries down there at the bottom of the garden. Even gods could be real, even the one of impossible contradictions and with such a desperate need to be worshipped as the one you were told about when you were still young enough to think such things were possible, even if never very likely.
It is possible to believe in magic and the possibilities uncovered by the power of the imagination when you are young. When you are young, everything is magical, even the morning seems so full of wonder, whether you wake up to a sun-filled day or discover the whole world hidden under deep white blankets of snow.
As you grow older and the mornings lose their magic, becoming just another great lump of hours you have to wade through on the way to the rest of your life, magic seems to have faded away. You no longer expect unicorns, ride on dragons or to meet Oberon and Titania in the deep woods… and as for those sad, needful gods… well, really.