The idiom of "doesn't grow on trees" as a metaphor for scarcity falls apart when you realize that food does grow on trees yet is still very scarce.

Extremely not-fun fact: collectively, humanity currently produces more than enough food for every person. But a huge part of it is either wasted or inaccessible by people that need them, which usually results in them not going to anyone and being wasted, which is why we still have food scarcity.