To Write it Down on Paper or on a Digital Device
One quick way to determine whether you should write your thoughts down on paper or on a digital device, is to ask yourself this question: “Am I concerned about someone else reading this?”
If the answer is yes, then definitely write it down on paper and not on a digital device. And definitely don't put it out online.
Yes, I understand that leaving your notebook laying around is not safer than say, an encrypted note-taking app. But to that I will say, don't leave your notebook laying around for other people to pick up.