Earlier quoted context omitted.
You're right of course but you get what they _mean_ right? Persistence can be key to accomplishing something significant you don't feel capable of. Or am I being too charitable?
That specific example seems more like some combination of persistence and power is required: great power suddenly and temporarily expressed could cut through stone while a weak power expressed over a long-enough time frame would have the same effect. On it's face it's only a partially true statement and thus is effectively 'BS' when presented as an aphorism. As well, it anthropormorphizes the effect of gravity on wat…
That's what it's intended to do. It's not trying to be a statement about Geology.