WMG / Bewitched

Samantha divorced the first Darrin for being a lousy father who purposely stunted his daughter Tabitha's magical development. Samantha then quickly married a second mortal whose name was Darrin so her daughter would not have to go without a father figure; and Samantha met him at the first Darrin's workplace, being too much of a busy homemaker to find a replacement elsewhere. Naturally, since she found another guy in such a short time that it was seamless, this guy was as big a jerk as the first guy, and also discouraged Tabitha from developing and using her witchly powers. Samantha keeps marrying jerks because she's a nitwit who drank martinis when Tabitha was still in Sam's womb. Good thing Tabitha has her good loving grandmother.
  • This is Jossed by the fact that the new Darrin had the same parents as her old Darrin.
  • The same mother anyway. The father was played by multiple actors so maybe they're half brothers.

Samantha and Serena were switched at birth.
Serena could totally be Endora's daughter. Aunt Clara is Samantha's real mother.

Samantha used her magic to change Darrin's appearance.
Samantha has shown herself to be very protective of her husband, and may have changed the way he looks to prevent other witches who have antagonized him over the years from realizing who he was so they would leave him alone. Of course, her relatives would be none the wiser, but that was unavoidable.
  • Another possibility: Apparently Dick York was replaced because his back was so bad that he couldn't act on the show anymore and spent many episodes soon before his departure just lying down. Maybe Darrin's body was failing him and making it hard for him to move around. Samantha used her magic to give him a new and healthy body.

Magic is symbolic of masturbation.
Samantha vows to stop as symbolized by her marrying of an uptight non-magical man. The couple usually keep their daughter, Tabitha, from using magic. Nonetheless, Sam and Tabitha use magic at times when alone. Sometimes magic seems taboo. Aging sometimes alters magical ability and control.

Every case of The Other Darrin on this show was actually The Nth Doctor
Aunt Clara screwed up one of her spells and turned Dick York into Dick Sargent. She ended up doing the same thing to Louise Tate, Gladys Kravitz, and Darrin's dad, too. With some help from Endora, she altered everyone's memories as well as all pictures so that everyone (even Sam) thinks that's what they always looked like. Clara was going to undo all the damage later, but she accidentally turned herself into Esmerelda. This explains why Clara is neither seen nor mentioned in the later seasons.

Witches are normally polyamorous
The question of whether Endora and Maurice are, or ever were, formally married is never outright stated. They do not live together but are not explicitly divorced. In one episode, when under the effects of a love potion Endora nearly marries one of Darren's clients, without any mention being made of her needing to divorce Maurice first. The love potion in question was intended to make Samantha fall in love with her warlock ex-boyfriend and leave Darren. No mention is made of the ethical or moral ramifications of using magic to cause someone to commit adultery and breakup their current marriage. Meanwhile, most of the other witches and warlocks that appear on the show seem to be single, including all of Samantha's family.
  • Fridge Brilliance: This would actually explain why Samantha would want to marry a mortal. This way, she gets a loving husband who belongs all to herself.

Bewitched is actually the tragic story of a woman suffering from a severe mental illness, namely...
...Capgras delusion.

As The Other Wiki indicates, Capgras delusion is a mental illness that makes people believe that their friends and loved ones are being replaced by lookalikes. Samantha Stephens, a woman with an already fragile mental state, ends up suffering a severe break from reality when she marries a man that her parents don't approve of (Darrin). As a result, she starts claiming she is a witch, as is everyone in her family. She's put into a gated community of non-dangerous psychotics, which is run by a man named Doctor Bombay, for her own safety; Gladys, her next door neighbor, has acute paranoia. The crazy incidents of the show are actually various doctors trying different modes of therapy and role-play to try to heal Samantha's broken mind; that's why Darrin constantly pushes Sam not to use her "witchcraft." As time passes, her Capgras delusion begins to manifest in small ways—her husband's boss's wife is the first person to be "replaced," followed by her father-in-law. Things start looking up when she has a baby...but then the child shows signs of suffering from mental illness. This wreaks havoc on Samantha's mental state, which manifests as Gladys being replaced in her mind as well. When Samantha becomes pregnant again, her fear of this baby turning out "wrong" drives her totally over the edge, and her own husband becomes a total stranger to her. This is why so many of the later episodes seem similar to early ones—the psychiatrists urged Darrin to try to recreate scenarios in which Samantha was more stable. The one person in Samantha's life who constantly supports her is Endora—she visits almost every day and encourages her to do whatever is necessary (including engaging in her witchcraft delusions) to avoid pain—which is why she maintains her identity through the whole run of the show.
Bewitched takes place in the Potterverse.
Evidence is up to you.