The difference is that everyone who wants to build in California has to follow the same rules and wear the hard hat.
If you don't believe me, walk by a construction site in Manhattan and ask the guy in the hard hat.
The hard hat was to protect him should the parents swoop low.
also hardhat, hard-hat, late 14c., "helmet;" 1935, "derby hat;" meaning "safety helmet" is from 1953; used figuratively for "construction worker" from 1970.
: Caution, this is a hard-hat zonenoun phrase
[the political sense fr the vocal and sometimes violent opposition of many construction workers to the US peace movement during the Vietnam War, reinforced by terms like hard line and hard core]