Quick answer
Property comes down through a family. A good marriage does not, and the verse says where it does come from.
Read both lines
The contrast is between two kinds of receiving. An inheritance is arranged, expected, and traceable to a person who died; nobody is surprised by it. The second line puts a wife in an entirely different category, not earned, not arranged by a family, and not owed. Placing this immediately after verse 13 is the chapter's own answer to what verse 13 described, and the placement looks deliberate. What the verse does not do is turn marriage into a merit system, and it is not a promise issued to anyone still waiting. It says only that the good thing, where it exists, arrived as a gift, which is a claim about the giver rather than about the man who received it.
Related: Proverbs 18:22 · Proverbs 31:10 · Proverbs 12:4 · James 1:17
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.