You go into the kitchen to prepare tea. You are certain you decided this, and that you are doing this. Let us investigate this presumption.
Prior to going into the kitchen, you were involved in some other task. And then the thought: “I want some tea” occurs. The thought “I want some tea” instigates the action of going into the kitchen to put the kettle on. Pretty elementary.
But let us look closer. Let us forget about the action and look at the thought. The ultimate clue to who dunnit, lies with the thought. Prior to the arrival of that thought, where was it? What mechanism spawned it?
A likely answer is “the brain”. But even that thought: “Thoughts come from the brain”, where did that come from? Do you even know what your next thought will be? Give it a shot.
If you don’t know what your next thought will be and you are finding it challenging to figure out where they come from and actions arise from thought, then isn’t going into the kitchen to put the kettle on just happening?
So who dunnit?
Investigate this yourself.