Since my childhood, I have been hearing from my parents that we should not cut hair or nails on Saturday. You should not shave also on this day. When asked why, they used to tell me that it brings bad luck as it brings anger of Planet Shani (Saturn) upon us. We lose money and peace of mind in our life. This belief is very common amongst Hindus, and hence, most of the Hindus do not cut hair or nails on Saturday.
The answer seems reasonable for those who believe in Astrology and do not like to question the traditions. Those who are not satisfied by the answer always try to find the actual scientific reasons behind such things.
Possible reasons behind not cutting hair on Saturdays:
1. It is believed that cutting hair/nail would bring bad luck to the person because it would attract the anger of Planet Shani, which is considered as a deity. In Indian Astrology, Shani has great importance in terms of human life. It is believed that all the bad things that happen to us are because of Planet Shani. Especially, in Kali Yuga, Shani is very powerful and even deities have to suffer from his anger. Hence, it is advisable that one should get his/her hair/nails cut on Saturdays.
2. The second most probable and logical reason could be that in old times, the people from barber caste used to do the job of cutting hair and they had no weekly offs. Hence, in that way, they used to get a weekly off on Saturday. Plus, many people in India prefer to cut hair/nails on Sundays. In general, there used to be only one or two barbers in a village. Therefore, on Sunday the workload would be maximum and therefore, they were able to relax and prepare themselves for the rest of the week.
There could be many other reasons behind it. We cannot tell anything certainly today. I have seen many people cutting their hair and/or nails on Saturday and nothing bad happens in their lives. Many businessmen and executives have to shave everyday; still they are earning heavily and living a good life. Problems will always be there in our lives whether you cut your hair on Saturday or not. It is our attitude that matters.
We should remember one that things change with time. This tradition could be right for the old time. There could be some reason behind it but now a day, it seems useless. Hence, we should get off such things from our minds.