What is the primary factor that fatigue can impair?

Fatigue primarily impairs alertness, which is crucial for maintaining focus and responsiveness in various tasks. When someone is fatigued, their ability to notice important cues, react promptly to situations, and sustain attention over time diminishes significantly. This reduced alertness can lead to slower response times and an increased likelihood of errors, which is especially concerning in situations requiring vigilance, such as driving or operating machinery.

While fatigue can also affect cognitive reasoning, physical exertion, and communication skills, these effects are often secondary to the impact on alertness. Therefore, maintaining alertness is fundamental to ensuring performance across various domains, making it the most significant factor affected by fatigue.