More seriously, ADHD, among others, is a working memory disorder. A way to cover this is to use "prosthetics" for it, such as a notepad that you always carry with you. If this affects you strongly, train your muscle memory to use it to note down what you were planning to do and to refer to it when you forgot.
In PC-speak, ADHDers have traded RAM for more CPU.
Of course one solution doesn't work for everyone. if you current system works for you, keep at it. I know for me, fishing the phone out my pocket, unlocking it, opening a notepad app, opening a new note and typing it badly, is probably as slow as a notepad at least. And then due to the nature of the phone, I forgot I had notes.