Guruji, they say one should not step out on the night of Amavasya (new moon). Why is that?

Sri Sri Ravi Shankar:

In the ancient times, it used to be extremely dark on the Amavasya night and there was no electricity. People used to advise against going out so that one does not accidentally step on a snake or fall into a ditch. Even then, it is not that one should not travel on the night of Amavasya.
There is some effect of planetary positions also.