Fear, a common phenomena
No. 6 and 13 are feared by many. According to western mythology it is connected to Satan, the dark lord. But in Vedic Puranas, it is mentioned clearly that everything in the universe is dualistic in nature. What we think of as bad can become good in an instant and vice versa. The lack of this understanding is what causes unnecessary fear.
No. 6 in numerology is ruled by Venus (Shukra).
Shashti, the sixth tithi in astrology is also ruled by Venus.
Friday, the sixth day in a week is once again ruled by Venus.
What is Venus? It is the planet of prosperity. It is ruled by Goddess Lakshmi, the Goddess of prosperity.
No. 6 in tarot represents lovers.
Carbon, the 6th element of the periodic table acts as the basic building block of our physical life.
As you can see above, everything associated with no. 6 have a lot of creative energy. Yet, they all have an other completely different side. For ex., Venus, the planet of love & prosperity is also the Guru of Asuras, the representation of greed & lust. Carbon, the creator of physical life can also become the destroyer if it reacts with other elements (causing global warming and natural catastrophes). Virgo, the natural healer is also a natural malefic. Saturn, the planet of longevity is also the planet of fear and death (mrityu karaka).
The 3rd eye chakra aka Ajna chakra is the sixth chakra, the subconscious mind that connects you to the ultimate reality aka the Brahman. Humans are different from other species because we're the only species with sixth sense.
No. 13 in numerology is ruled by Rahu, the mystery healer.
Trayodashi, the thirteenth tithi in astrology is also associated with Lord Rudra, the God of dharma, thus we celebrate Pradosham on that day.
Hasta, the 13th nakshatra is known for its magical healing abilities.
No. 13 in tarot represents major transformation.
As you can see above, everything associated with no. 13 have a lot of healing and transforming energy. Yet, they all have an other completely different side. For ex., Rahu is also known as micro organisms such as viruses. Lord Rudra is also known as the destroyer among trinity, he destroys adharma (injustice) to bring dharma (justice). Hasta is also known for its trickeries and obsessions.
These numbers not only bring fear but also bring luck, love, creativity, rebirth, transformations, and confidence. So these positives and negatives are there for a balance. Happiness won't be there without sadness and vice versa. They both balance and compensate each other. Thus one has to understand the duality of the world. Nature shows this in many subtle ways. For example, rose, the beautiful flower is also covered by thorns. Nothing is entirely good or bad. The lack of this understanding is numbing the minds and hearts of people which is nothing but a great burden to the entire society. This is why it is said that even the Amrit (divine nectar) kills you if you take it too much.
Moral: Fixation on an idea without proper investigation is poisonous. It is against the process of evolution. You've to question everything and evolve constantly. That's why, people with fixed lagnas (taurus, leo, scorpio and aquarius) get 9th house as obstacles. Because 9th house represents evolution.