What factor can decrease the effectiveness of a knot by half?

Neglecting to dress the knot can significantly decrease its effectiveness because a properly dressed knot ensures that the lines or ropes are aligned correctly and evenly distributed throughout the knot structure. When a knot is not dressed, it can result in uneven stress distribution and can cause components of the knot to slip or become misaligned under tension. This misalignment can lead to a reduction in the knot's holding power and stability, thereby potentially decreasing its effectiveness by as much as half.

Dressing a knot involves adjusting its components so that they sit neatly and tightly against each other, which enhances its overall strength and reliability. A well-dressed knot ensures that the friction between its elements is maximized, allowing it to perform as intended during use.