Why is opening an umbrella indoors considered bad luck?

In one theory, early Egyptians believed that umbrellas protected noble and religious people from the sun and evil spirits. According to them, it was believed that using an umbrella indoors can offend the God of the sun.

The early Egyptians believed that the goddess Nuit enveloped the sky like an umbrella. As a result, the shadow that surrounded the person who used the umbrella was considered sacred, and stepping inside it by a unnoble person was considered a bad thing.

In the 18th century in Europe, when umbrellas with metal spokes became popular, many people accidentally injured themselves or broke objects when they opened them indoors, as they were hard to handle. Some people believe this is how the superstition started.

In another theory, it’s believed that people avoided opening umbrellas indoors because when they extend, they can easily break fragile objects. As a result, people used to warn each other about using an umbrella indoors, and thus it turned into a superstition.

Some people believed that umbrellas can be used to protect the person against storms in life, and that opening an umbrella indoors can offend the guardian spirits in the house, thus encouraging them to leave the person unprotected.

In 1883, it was believed by English people that holding an umbrella above the head indoors is a sign of death, and that death can happen in the house that uses the umbrella inside.

According to psychologists, when a person focuses on a certain belief, they are very likely to pick evidences to prove that it’s correct. If a person believes they will have bad luck if they open an umbrella indoors, the umbrella will be blamed if anything bad happened to them. (See Why is breaking a Mirror considered bad luck)

In the 19th century, when umbrellas were still big, opening them in houses resulted in some accidents because of their size, which led to many family arguments that were considered bad luck.

In the 19th century, many umbrellas were black, and as a result, they made people who used them indoors look like mourners in a graveyard. Some people started getting unpleasant feelings as a result, and so the superstition might have been born that way.

According to psychologists, humans like to feel in control, and they can sometimes use superstitions to reach that goal. By not opening an umbrella indoors, a person can rest assured that they will not have bad luck. (See Why is spilling salt considered bad luck?)