Kill Your Darlings
As an artist, sometimes you form emotional attachments to certain elements of your work (This is particularly relevant to my work in video production/photography/filmmaking).
Problem is, sometimes those emotional attachments, we'll call them "Darlings", can stand in between you finishing the project on time or in the case of video edits, getting your edit to a watchable length.
Just because you're in love with a shot, doesn't mean it's serving the edit. You've got to be able to take a sober look at your edit, get someone else's insight on it, and then if need be, kill your darlings.
Abother grwat example may be in songwriting. Unless your name's Bob Dylan, you probably don't need more than 3-4 verses to a song (if you want to keep it short and catchy) and you may have to kill your darlings. It's about making hard decisions about what to keep and what to let go.
This was taught to me by Jonathan Jermyn, the first hire I ever made at Rhino, and was taught to him by his former Director, Andy Lee... who we just started working with on a series of international filming projects. (Really sweet full circle stuff)