Every human being seeks happiness. The great irony this verse reveals is that happiness isn't found when we chase it directly for ourselves; it's found when we plan it for others.
The End of Whoever Plots Evil
The text says whoever plots evil will end up badly. Evil is corrosive. Before harming the victim, malice, revenge, and envy destroy the container where they're stored (the heart of whoever plans them). It's impossible to be happy while cultivating mental poison, even if you have a lot of money or power.
Working for the Good of Others
Notice the verb "work." Happiness takes work! It requires intentionality in serving, in solving other people's problems, in counseling peace.
Happiness as Immediate Reward
The translation you chose says these people "will find happiness." This happens here, on this earth. When you see the smile of someone you helped, or the peace restored in a conflict you mediated, a supernatural joy floods your soul. Neuroscience calls this the release of oxytocin and dopamine; the Bible calls it "the joy of the righteous." Want to be happy today? Make someone else happy.