Belief of Tamilians:-
Tamilians consider Amavasya auspicious and thereby start a new venture and do not hesitate in initiating anything new. They consider this day a period of growth and power. On Amavasya, there will be no moon however very next day one can see a moon and this signifies growth and thus they want their work initiated to grow and become successful. It is a growing phase of the moon.
In Sanskrit language word 'Ama' means together and 'Vasya' means dwelling. Thus it means dwelling together and togetherness means strength. It is the day when dead ancestors are worshiped and with the blessings of ancestors, if any auspicious activity is carried out, the chances of its failure are very less. A lot of religious activities are carried out on this day like taking a dip in holy rivers, fasting, performing sacrifices, feeding the poor and offerings are paid to the Gods. These all acts are believed to wash away sins and lend blessings of ancestors and God. Tamilians believe that when body, mind and heart are under control then no goal seems unattainable.
Belief of Other Hindus:-
According to Garuda Purana, Amavasya is inauspicious and thus no new work should be started on this day except Karthika Amavasya which falls on Deepavali. People do not travel on this day and workers do not work. They believe that since there is no moon, there will be rise in evil powers and black magic. These evil powers will do not let our auspicious work become successful and those traveling fear of some uncertainty and thus do not opt to travel on this day.