Tenacious
Happiness is a circle that's tenacious. In other words, we're all in this circle/cycle where we do whatever we can to grab onto happiness and hold it as tightly as we can.
しゅう, しつ
と
None
Happiness is as tenacious as a shih tzu (しつ) with a shoe (しゅう). That little dog does not want to give up on the shoe, no matter what's happening around it.