Kill your darlings
Also said as Cutting
Cutting something you love because the game is better or more finishable without it. The advice comes from writing: Arthur Quiller-Couch told students to "murder your darlings" in a 1914 lecture.
The things you are most attached to are the ones you are worst at judging, particularly if they took months. Time already spent is gone either way.
Say it
“I love the grappling hook too, but it took fifteen weeks and scored lowest in the playtest. Cut it. We can use the time on the boss fights people actually mention.”
Where you’ve seen it
Blizzard spent about seven years on a massive online game called Titan, then cancelled it. The team that remained took some of what it had into a far smaller idea, and that became Overwatch.
Not to be confused with sunk cost
Sunk cost is the trap: keeping something because of what it has already cost. Killing your darlings is the way out of it.