In my old plane the equilibrium is so delicate it's almost an artform onto itself. As you trim, the tab, which is just on the left side of the elevator, induces an ever so slight roll. I'm talking a degree every second month, or something equally slow
To compensate for this, I add the most subtle rudder trim.
But one tiny ascent, gust, descent, roll, trim change and the whole delicate balance is off. It becomes this elusive nirvana one keeps chasing. It never lasts. But it's great fun trying to keep everything in balance perfectly.
Just as roll's secondary effect is a move around the vertical axis, rudder's secondary effect is a move around the horizontal axis - rudder is also roll.