I like planting trees as a metaphor (doing something now that will last into the future after we’re gone) and as a Good Thing (because: #treesaregood). For the actual planting part, I’m good when they’re below a foot tall. Maybe two feet. It’s that “Dig a hole at least twice as large as the root ball” instruction, that never includes “…but first, pick an area that has never grown a tree in the last 50 years, to avoid having to spend so much time cutting through roots that ‘twice as big’ becomes a steadily diminishing size.”