Needs pinching back to stay full

What's happening

Tradescantia naturally races outward along a few long trailing stems and leaves its base bare as it ages. Each stem keeps extending from the tip, so even a healthy, brightly lit plant thins out in the center and looks straggly within a season or two if it's never cut back.

How to fix it

Pinch or snip each stem back to just above a leaf node — the little joint where leaves meet the stem. Cutting there pushes the plant to branch into two new shoots below the cut, so it bushes out fuller over the next few weeks. Trim the longest, barest stems first. Don't throw the cuttings away: Zebrina roots almost effortlessly, so poke a few cuttings straight back into the same pot's soil and they'll root in place to fill the bald center.

This is general guidance based on common symptoms; individual plants vary.