The phrase "comparison is the thief of joy" is true and slightly useless. It tells you the cost without explaining the mechanism. The actual problem is that comparison happens faster than consciousness, and what gets compared is structurally unfair.
Most upward comparison — looking at people who appear to be doing better — measures your inside (everything you know about your life: the doubts, the failures, the rough mornings, the parts that haven't worked) against their outside (the curated, intermittent, sometimes outright false sliver they let you see). That comparison was lost before you noticed you were making it.
The brain is wired for it. Tracking relative standing was once survival-relevant — knowing where you sat in a group of 150 people was useful information. The capacity to do it was a feature, not a bug. The environmental change is that we now do it against several thousand carefully-curated peer outputs a day, with metabolic equipment built for an order of magnitude smaller comparison set. The wiring is the same. The fuel is different.
What helps isn't to never compare. That's a non-starter. It's to recover faster. To notice the comparison the moment it's started, to recognise the rigged measurement for what it is, and to come back to your own life — your specific work, your specific people, the next thing you'd be doing if you weren't measuring.
People who do this well aren't immune to looking. They get out of the comparison loop quickly. The mood-drop is shorter. The hour lost doesn't become two. The thread of their own life stays warm while they look sideways briefly.
Looking is fine. Vanishing each time is the cost.