Is it true that whenever harm and benefit are estimated, and the harms outweigh the benefits, it is said to be unlawful? And must the questioner seek another job, given that their current job, with its rotating night and day shifts, has its harms outweighing its benefits?

The Sharia prohibits everything that harms a person and damages him in his religion or worldly life. This is indicated by the saying of the Messenger of Allah, peace and blessings be upon him: "There should be no harm nor reciprocating harm," and by the verse: (And do not throw [yourselves] with your [own] hands into destruction).

Working in shifts differs from smoking in that smoke is inherently harmful and causes deadly diseases, whereas staying up and working at night and changing sleep hours is among the permissible acts. If it causes harm, it varies among individuals.

If it is proven that this act is harmful to a specific person, he should avoid it and seek another job. In fact, it becomes obligatory for him to do so if he is clearly harmed by it. If the harms in your work outweigh its benefits, then leave it and seek a more suitable job for yourself, while ensuring the availability of a suitable alternative.