“Objects in mirror are closer than they appear.” This message on the passenger-door mirror reminds drivers that what they see is not necessarily what they get. This convex mirror offers a greater field of vision than the flat driver’s-door mirror but at the cost of compressing the view, thus making objects appear to be smaller and hence further away from the viewer than they actually are. Competent drivers learn to adjust to this helpful distortion and compensate accordingly. Similar problems of understanding what was seen and why it might appear as it did faced those who used convex lenses to increase the size of objects under the microscope.
Bynum H. The Microscope and the Eye: A History of Reflections, 1740-1870. JAMA. 2008;299(16):1957-1963. doi:10.1001/jama.299.16.1962