The five days between Yom Tob of Sukkot and Shemini Atzeret are referred to as 'Chol haMoed'.
Chol haMoed days enjoy an intermediate status between Yom Tob and regular work days. The rabbis prohibited certain type of works on Chol haMoed in order to allow time to enjoy the festival and study Torah, with one's family members.
The prohibition of work on Chol haMoed differs from the prohibitions of work on Yom Tob or Shabbat. The rabbis were very lenient and formulated various exceptions contemplating people's practical needs. An illustration of this type of exception:
The rabbis authorized 'Dabar ha-Abed' work done so as to avoid a loss.
Irrigation of a field is a type of strenuous work which will be normally prohibited on Chol haMoed. However, if the produce of a field will be lost if not irrigated, irrigation is permitted.
This principle is also applied in the world of business. One is allowed to work if by not working he will incur in present or potential losses, or to earn money that is needed to forestall a loss.
In the case of an employee, if someone were to take a week of unpaid leave, and thus not have enough money to pay the rent or mortgage for that month, then he/she is permitted to work.
Also, if not working would jeopardize one's job, or his realistic chances of promotion, a person may work.
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