Ink creates permanence, forcing you to be sure about what you put down– you can’t erase it.
When you write in pen, you’re signaling commitment.
Like a tattoo versus a sticker.
I used to only use pencils– and I had binders and binders full of notes in smudgy pencil.
But I found that I hardly even erased anything– though the thought of being able to do so was comforting.
And come to think of it, I hardly ever revisit my notes– do you?
Using ink is like formulating a strategy, while the pencil is for tactical adjustments.
You better be sure of your strategy and not be changing it every 10 minutes.
If you only have a pen, you’re forced to choose to write down only the things that you’re sure enough about that they’ll still be true in 10 years.