When they are defying you and just threw food over the kitchen, you'll get grey hairs trying to fight the urge to blow your top. You'll say things you promised yourself you would never say, because you're all out of ideas how to handle a tiny creature who is intent on riling you, just to see what it's like.
Then they'll get sick and you'll need to carry them to a doctor and entrust them to medical staff you've never met, and you'll be so anxious you won't eat or sleep.
Then the next day you'll have the most wonderful conversation where your little charge asks you about the universe and you try and explain it to them, not knowing where to start or how much understanding they really have.
One thing though, you'll learn compassion, forgiveness and patience like you never thought possible.