Why a "high-gain" antenna isn't necessarily radiating more total power than a low-gain one fed the same input.
Feed 10 watts into two different antennas and it's tempting to assume the one with the bigger gain number on its datasheet is simply "stronger" in every sense. It isn't. Gain and efficiency answer two completely different questions about what happens to that power, and confusing them is one of the most common mistakes in RF system design — the kind that leads to underestimating coverage in some directions and overestimating it in others.