⚑ One of the most weaponized verses in the book. Read what it says and, just as importantly, what it does not.
Quick answer
Pressure reveals capacity. The saying is a compact observation about where a person's real reserves show up, and it is not a verdict on anyone's faith.
Read both lines
The Hebrew is a pun and English cannot keep it. The day of adversity is יוֹם צָרָה, tsarah, and the word for how small the strength turns out to be is צַר, tsar, from the same root, meaning narrow or constricted. So the sentence closes on itself: in a tight day, your strength turns out to be tight. That compression is the craft, and it also tells you what kind of saying this is. It is an aphorism, short and closed, of the sort that gets said once and remembered, and it is not an argument or a diagnosis.
What it observes is true and worth having. Nobody knows their own capacity in easy weather, and difficulty is the only instrument that measures it. The book has just said in the preceding saying that wisdom increases strength, so this verse is not despair. It is the other half of that claim, said with a shrug.
What it does not mean
This verse is not a test of anyone's faith, and it must never be used on someone who is struggling. The book of Proverbs is not describing a spiritual failure here and it names no consequence, no guilt, and no remedy; it simply says that a small strength shows up under pressure, which is a fact about reserves rather than about character.
Two uses have to be ruled out plainly. It is not a rebuke for depression, anxiety, grief, illness, exhaustion, or trauma, all of which can flatten a person entirely and none of which this verse is discussing. A body or a mind that has run out is not a soul that has failed, and no proverb overrules a medical reality. And it is not a tool for judging another person's collapse, since the saying is addressed in the second person to the reader about himself. Anyone using 24:10 to explain someone else's breakdown to them has taken a two-line observation about self-knowledge and turned it into an accusation the sentence cannot support. The very next saying in this collection commands the reader to go and rescue people who are being carried toward death, which is a strange thing to place beside a verse about contempt for the weak.
Related: Proverbs 24:5 · Proverbs 24:11–12 · Proverbs 18:14 · Proverbs 12:25
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.