Black Ice

[dukealien]

decided to ignore the reference in your spoiler in my interpretation : )
i think your metaphor fits for workings of single individuals.
you can "melt" the soft parts but the frozen, hard parts, hidden in the shadows are more resistant.
love how the metaphor is extended over/ below bridges.

Good to know it can be taken in a (what some would find) less offensive way.  And another interpretation for the collection (g).

Under bridges is usually less of a problem than on them - the distance is shorter,  vehicles don't have to time to get into an established skid or spin.  But being in the shadow of the span,  it tends to last longer there:  sun can still act on other black ice exposed to it.  Which is a little too involved for short form.

Thanks to all.