Here's why:

* Photosynthesis: Grass, like all plants, uses sunlight to power photosynthesis. This process converts light energy into chemical energy, which is used to create sugars for growth and development.

* Chlorophyll: Grass contains chlorophyll, the green pigment that absorbs sunlight for photosynthesis.

* Lack of sunlight: Without enough sunlight, grass will become weak, pale, and may even die.

However, the amount of sunlight needed varies depending on the grass species and the climate. Some grasses thrive in full sun, while others prefer shade.