Fair point, but basic physics has been a part of our education program for at least 60 years. Also for few years the ‘exchange priced’ or ‘market valued’ electricity has been somewhat popular and on the news, which adds up to the general understanding as if you know your stuff it means quite literal money as your bills are smaller. So, maybe ‘absolutely everyone’ is a bit of a stretch, but in general the majority of adult people understand the concept.

And also a ton of common folk understand it at least a bit on a deeper level as basic physics is included to studies beyond elementary school regardless on what you study. Sure, not everyone understands (or cares) how 3 phase AC in here adds up to 400V or why you need to have 2,5mm² wires for 16A fuse, but it’s still pretty common that people, specially in a separate house, understand how you can only pull 2300W out of a 10A circuit or 3600W from a 16A one (10 and 16A being the most common fuses in a household in here).