"Professional photographers know they need to backup their photos."
A homemaker or techie moonlighting for extra income aren't really 'professional photographers'. They may take photographs that look professional, but it's not the same thing.
One might say that professional developers use version control, then have counter examples of "well, this web design student doesn't ever uer version control, but she's the only person working on the code, so it doesn't matter". This is not a professional developer, even if she is capable of producing results that look like they were done by a professional.
A professional, imo, is defined as much by their habits and practices as by the output.