Your art is always mistake-free
Zentangles are meditations through pen. It’s a kind of drawing that much more about feel and intention than looking like a particular object or scene. Take a look at some examples.
And lastly, they are mistake-free. If you make an unintentional mark, it is all just part of what the final product will eventually become, and since you don’t know what that is, it can’t really be considered a mistake.
I love this part of the description. So much of creativity or art is stunted by our own quick judgements — thinking something is ugly or wrong. Zentangle is a way to let go of that judgement and just make marks for the sake of making marks, a bubble bath or hot tub for the usually analytical brain.