Vivid metaphor: grass growing on top of an old wall has nothing anchoring it sideways, so it bends whichever way the wind happens to blow. The full proverbial form is
墙头草，
两边倒 (qiángtóucǎo, liǎngbiān dǎo) — 'wall-top grass, leans both ways' — applied to politicians, employees, or anyone who lacks loyalty.
