There's a lot in this world you don't know, like if mermaids are real or if aliens actually exists, or when you will meet the one and only, your soulmate, or who to trust and who to not trust. You will never know this until it happens, until you experience them firsthand. You won't know if you don't take a leap of faith, have hope and really try.
But then there are things that you do know, like how one plus one equals two and how the earth is round and not flat. You know stuff like how scary it is to really trust someone, and how scary it can be to take that leap of faith. You know how terrifying it can be to leap and have hope for something when you know how easy it would be to just run away and hide from your problems, how scary it is to face the unknown.
That's how something you know can hide the unknown so openly, how the known can trick us into doing something we don't want, something we never wished for. Make us choose to take that small leap into the unknown without us knowing.
The known and the unknown go hand in hand, you can't only get one, if you choose the known you will get the unknown and if you choose the unknown you will get the known.
And that will always stay the same, the known and unknown are like that old married couple that seems to never die.