1.Ross "cheated" on Rachel during their ~break~ because he was taught a different definition of the term by Carol.
The theory is based on the fact that in one episode shortly after his divorce, Ross reveals that he lost his virginity to, and went on to marry, Carol. In a later episode, however, we learn that he also slept with a cleaning lady in college.
2.Ross lost custody of Ben because he was a terrible father.
Over the course of a few seasons Ross asked a self-defence instructor to help him scare women he was planning to attack, tried to kiss his first-cousin, dated his students, was signed off work due to uncontrollable rage and objected to employing a male nanny.
3.But he also may have just abandoned Ben to focus on his new family with Rachel.
4.Richard knew that Chandler was planning to propose to Monica, and that's why he rushed to profess his love and commitment to her.
The theory is based on the fact that Chandler checks his jacket pocket to ensure the ring box is still there moments before Richard enters the same restaurant.
5.Monica had the best sex of her life with Chandler because she literally taught him how to navigate her body.
Well, this theory explains the plot hole by referring back to the episode where Monica teaches Chandler the seven female erogenous zones, and the order in which to stimulate them.
6.Ross and Rachel were cursed for seven years in the pilot episode, and that's why their relationship was tumultuous.
7.The group always got the same table in Central Perk because Gunther secretly reserved it for Rachel.
8.Erica knew she was having twins but was worried Monica and Chandler would back out of the adoption if she told them.
9.Monica, Phoebe and Rachel having very different routes into motherhood was deliberate.
10.Phoebe was actually a genius with zero ambition.
The theory is mainly based on the scene in which Phoebe almost convinces Ross that the theory of evolution is flawed.
11.Chandler deliberately tricked Monica into the quiz so that he and Joey could win her apartment.
It posits that during the scene in which Joey and Chandler guess what's in Rachel's shopping bag, he steals a glance while walking over to tell Ross to stop his game show host impression.
After all, it's him who suggests this gamble in the lightning round of the game.