What can be inferred about visibility conditions when windshield wipers are necessary?

When windshield wipers are necessary, it indicates that there are elements in the environment that are obstructing the driver's view, such as rain, snow, or other forms of precipitation. These conditions create challenges in visibility, making it difficult for the driver to see the road and obstacles clearly. The use of windshield wipers is a direct response to these less-than-ideal weather conditions, highlighting the importance of maintaining good visibility while driving.

In contrast, clear conditions would not require the use of wipers, optimal driving conditions would mean that visibility is unimpeded, and occasional conditions suggest that the necessity for wipers wouldn't be consistent. Therefore, the inference regarding difficulty in visibility is clearly aligned with the need for windshield wipers.