Use all your mirrors, and consider a shoulder check when it’s not safe to rely on your mirrors alone – for example, to check any blind spot when reversing, moving off from the kerb, joining a motorway or leaving a roundabout.
It is physically impossible to achieve all-round visibility using only the mirrors. The coverage angle of your mirrors and your effective field of view do not sum to 360 degrees. You will have at least two blind spots to the side, two A-pillar blind spots to the front and in many cars additional rear blind spots.
Try it for yourself - sit in the driver seat of your car in a safe open space, then ask someone to slowly walk around the car in an outward spiral. It should become readily apparent that at certain angles and distances, they disappear from view entirely unless you turn your head.
