Quick answer
What the wicked man dreads finds him, and what the righteous man longs for is granted. The proverb observes the long trajectories of dread and desire under God's government; it is not a blank check for wishes.
Read both lines
The first line has the structure of a nightmare: the thing the wicked man fears "will come upon him," arrives, catches up. Wickedness lives braced. It knows what it deserves and spends its energy fencing that outcome away, and the proverb says the fence fails; the feared thing homes in. Job 3:25 sounds similar ("the thing I greatly feared has come upon me"), but Job's story is the canonical guardrail against running this proverb backward: Job was righteous, his suffering did not prove wickedness, and his fear did not manufacture what happened to him. The proverb describes where wickedness tends; it is not a mechanism by which fear attracts calamity.
The second line inverts everything: the desire of the righteous is granted. Given, not seized. The verb is passive, and behind it stands the LORD of 10:3, who casts away the craving of the wicked and will not let the righteous soul famish. The quiet assumption is that righteous desire has itself been shaped by righteousness; a heart oriented toward God wants, increasingly, the kind of things God delights to give (Psalm 37:4). This is an observed pattern of God's government, not a mechanism, and the righteous poor of 15:16 knew both truths at once.
Related: Proverbs 10:3 · Psalm 37:4 · Proverbs 11:23
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.