When does layering become overworking?

I keep hitting a point with coloured pencil where a passage looks luminous, the values are sitting right, there is actual light in it, and then I do one more pass and the whole thing goes flat. Dead waxy surface, no life left.

It happened again last week on a kitchen scene I have been redrawing (yes, the same kitchen corner, again). The copper pot had this glow to it and I wanted just a little more warmth in the shadow side. Three layers later the paper tooth was gone and so was the glow.

I find it so hard to stop while something is working. The urge to refine pulls me in every time. With graphite I can usually feel when the tooth is filling up, but with coloured pencil the shift from "enough" to "ruined" seems to happen in a single layer.

Does anyone have a way of recognising that tipping point before they cross it? Do you step back at set intervals, photograph it, put it away for a day? I would love to hear what actually works for you.