Well, maybe instant coffee isn't worth much (what's with that aftertaste anyway), but an unsparing critique is invaluable.
First, let's define "ruthless." For our purposes, it means momentarily putting pity aside to be honest, incisive, direct. But since text without context is pretext, we should also define "critique." I like Merriam-Webster's slant on this one: "the art of evaluating or analyzing works of art or literature" and "the scientific investigation of literary documents" regarding aspects like "origin, text, composition or history."
What I love about that definition is it takes into account that critique is both art and science, involves analysis, which means it takes time, and encompasses various aspects of a work, meaning it's not superficial. So, for our purposes, "critique" is a knowledgeable, well thought out, accurate and articulate assessment of a writer's work (not the writer). And I'd add that the most valuable critiques have the writer's best long-range interests at heart. Some observations hurt in the short run but are the difference between stuck in endless loop and progress in the long run.
There's another crucial aspect of the truly beneficial critique — it's usually delivered directly, face to face. In this way, the personal critique is a world away from a critique group, where mass opinion and a herd mentality can quickly warp even the soundest observation. Besides, it's a lot harder to slog through a ream of comments (and more demoralizing), than to bite the bullet and have a couple of people you care about, and who are qualified, read and comment on your work.
So, go on, have that cup of criticism — a spoonful of sugar, or agave nectar, will help it go down.