Add condensation and salt water, and you have nature's inexorable system at work to reduce everything back to basic elements. A person with average eyesight, even one of the guests, a member of the family or otherwise, can squint into an engine compartment and spot a wire that has had the insulation scraped against something sharp or see a buildup of corrosion on terminals or fastenings - if asked to look for it. These potential problems caused by the elements, chafing, abrasion or simply age are constantly developing in a boat. They are not usually serious, but they require attention. Sometimes strange things happen at sea that may have nothing to do with maintenance, but are brought about by the jarring of the boat in the waves.
Electrical failures are particularly frustrating and often sudden.
One second things are running fine, and the next you are dead in the water. Some problems, like a coil wire springing out of a coil, are unavoidable, but others can be prevented. The boater should always open the engine compartment and at least take a careful look at everything before leaving the dock. Begin with the easy stuff. Wires may need more clamps to keep them from chafing.