Quick answer
Generosity does not empty a person, and looking away costs more than giving would have. The second line names the actual sin as the looking away.
Read both lines
The first line's claim is deliberately modest: will not lack, not will prosper, so what is promised is sufficiency rather than return. That restraint keeps it from becoming an investment verse, and it matches 11:24–25, where the one who scatters increases and the generous soul is made fat.
The second line is the sharper half. Hides his eyes is a choice about seeing, not about spending, so the man being condemned has not refused a request. He has arranged not to receive one, which is how most of it actually happens. The chapter has already said the same thing from God's side at 21:13, where shutting your ears to the poor man's cry comes back around, and 28:8 said the extractor's money ends up with someone gracious to the poor. This verse locates the offense one step earlier than refusal, at the moment of not looking.
Related: Proverbs 11:24–25 · Proverbs 21:13 · Proverbs 19:17 · Proverbs 22:9
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.