Quick answer
Pride does the lowering itself. The verse makes it self-acting rather than punished.
Read both lines
תַּשְׁפִּילֶנּוּ, it will bring him low, with pride as the subject: the thing itself does the work, nobody has to arrange it. That is the same mechanism 16:18 states as pride going before destruction and 18:12 as a haughty heart before destruction, and 11:2 pairs pride with shame arriving.
The second line's verb is worth noticing. The humble in spirit יִתְמֹךְ כָּבוֹד, lays hold of or retains honor, an active grip rather than a passive reward. And 15:33 says the same sequence plainly, that before honor is humility. Four sayings across the book agree on the order and this one is the most compressed. Honor is not something the humble man is chasing, which is why he still has it.
Related: Proverbs 16:18 · Proverbs 18:12 · Proverbs 11:2 · Proverbs 15:33
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.