“Whoever gives heed to instruction prospers” just makes sense. But I’ll add that that it could also be translated “whoever gives heed to a matter finds good.” Just being diligent to any project or situation sets us up for good things to happen.
“And blessed is the one who trust in the LORD.” “Blessed” means “happy,” and I can’t think of anyone I know who “trusts in the LORD” and has decided it’s been a really bad way to go!
Admittedly, God doesn’t always give me what I want when I want it — in fact, He usually doesn’t! But, when the smoke all clears and the dust all settles, I’ve found that His plan and timing were so much better than my own!
This verse just sounds like a recipe for success: pay attention to things and trust the LORD. Good and happy things will follow!
But I suppose I should add a post-script. I do think we 21st century Americans sometimes have a twisted view of “happiness.” It doesn’t mean everything is going my way…it does mean that His supernatural “joy” will see me through all the realities of this life.
It’s like the last line of the complete Serenity Prayer says:
(See https://helpingupmission.org/serenity-prayer)