Professor 2 said something like this:
Every paper I write has three stages. First, I write a draft of the paper. That takes two sessions, and then I put it aside for a few weeks. Writing the draft tells me what I need to do, and in the next phase, I collect the material I need and get all the details. The third phase is the final writeup and submission.
Each month, I write a new paper draft. By always keeping papers in different stages, I can move on to do something productive right away while a paper is reviewed by a journal.
Right now I have 10 or 11 papers in different stages of progress, and that is about right. When I have that many, I don't care too much if a paper gets rejected, and don't waste time in getting angry or upset. Publishing is a very slow process, and I need to keep moving.
I'm not the kind of person that can sit and concentrate week after week on one project. I get tired. I need to put things aside and let them mature for periods of time.