Trinitron tubes suffer from being flat, in at least one plane. The end result is that the shadow mask (the perforated metal plate that guides the electron beam to the correct colour phosphor dots, for those that don't know about the innards of CRTs), isn't held in place by being in a convex shape, but is attached by two fine wires running horizontally.

They're about one third and two thirds of the way down the screen, and can be seen as two faint horizontal lines on a full-white background. Most people never see them until they're pointed out, then can never stop seeing them

Anyway, because of the construction, the shadow mask can shift very slightly, which distorts the image, sometimes going slightly unfocussed. I'd guess that the Sony Standard Whacking Tool (tm) is neatly calibrated to apply just enough jolt to pop the shadow mask back into position. It might work...

I would think that the force applied by an SSWT should be more along the lines of disciplining a small child rather than a donkey

pca