Why would a sailor be unable to use celestial navigation all the time?

A sailor may be unable to use celestial navigation all the time due to poor weather conditions, such as overcast skies or fog, which obstruct the visibility of celestial bodies like the sun and stars. Additionally, celestial navigation requires a clear horizon for accurate measurements, which can be difficult in rough seas or coastal areas. Furthermore, during certain times of the day, such as dawn or dusk, the position of the sun may not provide reliable information for navigation.