Looking at this again, I'm suddenly noticing the role of "knowing" in the quote. The understanding doesn't come from merely planting trees - it comes from planting them while fully conscious that you won't benefit. This suggests that it's not just the action itself, but the awareness and intentionality behind it that leads to wisdom.
There's something almost paradoxical here: the clearest understanding of life's meaning seems to come when we act in ways that transcend our own life. We grasp the significance of living precisely when we acknowledge and act beyond our own mortality. It's as if the acceptance of our temporal limits somehow expands our spiritual horizons.
I'm also struck today by how this might relate to education and teaching. Every great teacher, in a sense, plants seeds of knowledge and understanding that will fully bloom long after they're gone. The patience and faith required to be an educator mirrors that of the tree planter - both must trust in a future they can imagine but won't witness.