Give the character an obstacle
I adore this scene in Alice’s Adventures in Wonderland.
Alice has found a golden key lying on a glass table. At first, she cannot locate the door in which the key fits but then she discovers it behind a curtain. The door leads to a passageway, and beyond the passageway is a tempting garden filled with flowers and fountains. The obstacle? The door is 15″ high and Alice, a normal human girl, is nowhere near this size.
Alice then finds a bottle with a message on it: DRINK ME.
After some hesitation, being sensibly concerned that the liquid might be poison, she drinks the bottle’s contents and promptly reduces to a girl of ten inches tall, plenty small enough to fit through the door!
Alice forgot to take the key off of the table. She can’t reach the key now, because the table is towering above her! She solved the problem of her size, but what is the point of being small if you can no longer unlock the little door?
What a set of obstacles to give a character, don’t you think? A door that is too small…a key that is too high!