Nothing ruins a nice day on the water like a mechanical or electrical breakdown. While it’s true that there are components that can fail without warning, that are not considered maintenance items, rigid adherence to a preventive maintenance schedule is the best way to avoid unexpected failures.
Before leaving the dock (every time) check thru-hulls, raw water strainers, all fluids and all machinery spaces. After this, check for proper operation of all on-board systems. Don’t leave the dock until you are sure everything is functioning properly. Have a plan to deal with all the usual contingencies when on the water, such as a clogged fuel filter; cooling system issues; or unexpected problems with electronics.
Have a relationship with a reliable marine technician so that when you have an urgent need for assistance, there is someone who will take your phone call. Your relationship with a marine technician or boat service yard should be treated with ultimate reverence. If you are considerate of the people who work on your boat, they will be much more willing to help you out of a jam.