It's a belief, very similar to religion. From a rational point it doesn't make sense, but then there's no requirement to be sensible all the time.
You should not believe in Superstitions. Superstitions is the product of ignorance among people. Many superstitions are not true.
Yes, anybody that wishes to believe in superstitions can.
People believe in superstitions because they are driven by fear.
Possibly because they were religious. People who are not religious do not normally believe in superstitions.
I do not believe they are true.
Superstitions are beliefs supported only by rumor, not by factual observation. Rational people therefore do not believe such things.
Superstitions suggest that a twitching right eye can mean good luck or bad luck, depending on the culture. Some believe it signifies impending good news, while others see it as a warning of misfortune.
because
It has no survival value. People believe in in all kinds of things which others would consider superstitions. In most cases it does no harm.
They don't really. People who believe in superstitions are more prone to believe in the haunted houses thing than people who don't.
Yes, a lot of people still believe in superstitions, despite clear and contradictory evidence (or rational explanations for the origin of a superstition).
No they are just superstitions, you are crazy if you believe that..