An instrument rating entitles a pilot to legally navigate an aircraft when the weather is bad enough that he can’t see outside. A pilot who is not instrument-rated must always stay out of the clouds. If the weather is such that he can’t do that, he must stay on the ground.
The training required to obtain an instrument rating is extensive. In most cases, it takes a pilot longer and costs him more to obtain the rating than it did for him to get his pilot’s license in the first