The seven-day week originated in Mesopotamia among the Babylonians, and it has stuck around for millennia. However, it's not inherently special. Egyptians once used a ten-day week, and Romans used an eight-day week before officially adopting a seven-day week in AD 321.
Still, the seven-day week is so ingrained that we may notice how days "feel." I was recently caught off guard by a productive "Tuesday", realizing halfway through the day that it was actually Monday. Recent research shows that a big player in the psychology of weeks is a tendency to take risks.
"Across a range of studies, we have found that response to risk changes systematically through the week. Specifically, willingness to take risks decreases from Monday to Thursday and rebounds on Friday. The surprising implication is that the outcome of a decision can depend on the day of the week on which it is taken."Dr. Rob Jenkins for The British Academy
The article discusses the implications that weekly risk fluctuation may have on elections. Because the UK holds elections on Thursdays, the most risk-averse day, are voters more likely to support causes they deem comfortable and safe?
"The Scottish Independence and Brexit referendums were also held on Thursdays. The core message of the Brexit campaign – "Take back control" – was a direct appeal to risk aversion, and the opinion poll data show that support for Brexit was strongest on Thursdays. Our analyses show that the outcomes might have been different had they been held on Fridays."Dr. Rob Jenkins for The British Academy