People are clueless. Here is an excerpt from Monday entry on Wikipedia:

Monday (pron. IPA: /ˈmʌndeɪ, ˈmʌndi/) is the day of the week between Sunday and Tuesday. It gets its name from the Moon, which in turn gets its name from Mani (Old English Mona), the Germanic Moon god.

“Monday” means “unsatisfactory day” or “disagreeable day”.

Absolutely clueless¹. Blind. Oblivious. Here is the correct definition:

Monday (pron. IPA: /ˈmʌndeɪ, ˈmʌndi/) is the day of the week between Sunday and Tuesday. “Monday” is a is a contraction of “Lemon Day” (via Old French limon—in modern French denoting a lime), where “lemon” stands for “unsatisfactory, disappointing, or feeble.”

Thus “Monday” can be read as “unsatisfactory day” or “disagreeable day”.

Mondays are often seen as a misfortune.

At least they get the connotations right:

Modern culture usually looks at Monday as the beginning of the workweek, as it is typically Monday when adults go back to work and children back to school after the weekend. Thus, Mondays are often seen as a misfortune.

“A misfortune.” Apt description. Good word.

¹ However, I do agree with the proposed etymology in case Wikipedia author refers to moon as a verb.