Why a clear visual path isn't always enough for a radio link.
Stand at one tower, look toward the other, and see it clearly with nothing in between. Reasonable to assume the link is good to go — and that assumption is incomplete. Line-of-sight is a real requirement for most point-to-point microwave and high-frequency radio links, and it's necessary. It just isn't sufficient by itself. Radio energy doesn't travel down an infinitely thin beam the way a laser pointer or a sightline does — it fills a much wider volume of space around that direct path, and an obstruction that never touches the visual sightline at all can still degrade or block the link.