Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Nowhere in the Bible is Satan described as ruling over or being in Hell. Throughout the Bible Satan is described as constantly on Earth, and the Book of Revelation says that after Judgment Satan will be cast into Hell.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
The Immaculate Conception is not synonymous with the virgin birth of Jesus, nor is it a supposed belief in the virgin birth of Mary, his mother. Rather, the Immaculate Conception is the Roman Catholic belief that Mary was not subject to original sin from the first moment of her existence, when she was conceived. The concept of the virgin birth, on the other hand, is the belief that Mary miraculously conceived Jesus while remaining a virgin.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Nowhere in the Bible does it say exactly three magi came to visit the baby Jesus, nor that they were kings, rode on camels, or that their names were Casper, Melchior and Balthazar. Matthew 2 has traditionally been combined with Isaiah 60:1–3.
60:1 Arise, shine, for your light has come,
and the glory of the Lord has risen upon you.
For behold, darkness shall cover the earth,
and thick darkness the peoples;
but the Lord will arise upon you,
and his glory will be seen upon you.
And nations shall come to your light,
and kings to the brightness of your rising.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Three magi are supposed because three gifts are described, and artistic depictions of the nativity after about the year 900 almost always depict three magi. Additionally, the wise men in the actual biblical narrative did not visit on the day Jesus was born, but they saw Jesus as a child, in a house as many as two years afterwards (Matthew 2:11).

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Another popular myth is that having sex in the days leading up to a sporting event or contest is detrimental to performance. Numerous studies have shown that there is no physiological basis to this myth. Additionally, it has been demonstrated that sex during the 24 hours prior to sports activity can elevate the levels of testosterone in males, which potentially could enhance their performance.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Mental abilities are not absolutely separated into the left and right cerebral hemispheres of the brain. Some mental functions such as speech and language (cf. Broca's area, Wernicke's area) tend to activate one hemisphere of the brain more than the other, in some kinds of tasks. If one hemisphere is damaged at a very early age, however, these functions can often be recovered in part or even in full by the other hemisphere (see Neuroplasticity). Other abilities such as motor control, memory, and general reasoning are served equally by the two hemispheres.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Golgi-stained neurons in human hippocampal tissue. It is commonly believed that humans will not grow new brain cells, but research has shown that some neurons can reform in humans.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Until very recently medical experts believed that humans were born with all of the brain cells they would ever have. However, we now know that new neurons can be created in the postnatal brain. Researchers have observed adult neurogenesis in avians, Old World Primates, and humans. Adults of these species retain multipotent (see cell potency) neural stem cells in the subventricular zone of the lateral ventricles and subgranular zone of the dentate gyrus. The newborn neurons generated in these areas migrate to the olfactory bulb and the dentate gyrus, respectively, and are believed to integrate into existing neural circuits. However, the function and physiological significance of adult-born neurons remains unclear. Some studies have suggested that post-natal neurogenesis also occurs in the neocortex, an idea that is disputed.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Vaccines do not cause autism. Fraudulent research by Andrew Wakefield claimed a connection. The results could not be reproduced. Subsequently the research was shown to be flawed and fraudulent.