Oliver Burkeman is my favourite pop psychologist (click here for the full article in today's Guardian):
Apart from anything else, the "one focus" belief serves to inhibit action: if you believe you have to give up your job as a lawyer in order to become a screenwriter - because people have to have one job - you'll probably never become a screenwriter. If you spend one hour actually screenwriting, you already are one.
Seems fair enough to me...
Scriptnotes, Ep 350: Limerence — Transcript
18 hours ago