You do not need to know what you are doing in order to do something great.
Many amazing things have been created from nothing more than a single idea.
A plan is optional, but ideas are essential.
You can always devise a plan later, but ideas are transient and scarce.
The goal, then, is not to have the best plan, but to have the best idea.
This likely means having a lot of bad ideas as well.
You will not know which ideas are good and which are bad, however, without testing them out, without following through on them, and without being willing to fail.
Take risks, be playful, and try new things.
Leave the planning for later.
But never let a good plan get in the way of a great idea.