In his book Napoleon’s Hemorrhoids and Other Small Events that Changed History, Phil Mason documents dozens of small happenings over the centuries, many of which seemed insignificant at the time, that seemed to change the course of history. As stated in the book, one of its purposes is to prove that “…significant historical events are caused by significant and great causes.”

Below are ten seemingly insignificant events that had a profound impact on human history:

1. When Adolf Hitler was only six years old, he experienced such vicious nightmares that his doctor recommended his parents send him to a mental health facility. However, they declined the suggestion, worrying that authorities would discover the abuse his father inflicted upon him. Had he received psychological help at this young age, he may have been mentally sound later in life.

2. In the 1930s, when Ronald Reagan was beginning his acting career, he attempted to join the American Communist Party. He was refused admittance, with the Party citing his lack of political intelligence and potential. Had the Communists accepted Reagan, his name likely would have been smeared during the witch hunt for Communists in Hollywood, which in turn would have prevented a successful presidential run (if he even still had the desire to run with one of the major parties) in the ‘80s.

3. President Kennedy came close to missing his inauguration – and his presidency. For five whole days in 1960, a deranged postal worker waited outside of the Kennedys’ house so that he would be ready to drive his car (which was rigged with a bomb) into the President-elect’s. Fortunately, he only wanted to kill Jack Kennedy, and he did not have the chance to pull off his plan before the police arrested him for a traffic violation due to the fact that Kennedy never went anywhere without his two-week old baby in case a photo-op arose.

4. Nixon’s entire Watergate plan was blown by one piece of masking tape. A security guard discovered that two of the locks on the doors in the Watergate building had been taped open, but assumed that workers had placed them there to avoid keying in and out. However, it was only after one of the locks had been re-taped that the security guard became concerned and alerted the authorities, who discovered the break-in. Had the intruders avoided re-taping that one door, Nixon’s presidency may have taken a very different course.

5. In 1947, Fidel Castro came to the United States for a tryout with the Washington Senators. The team decided he was not cut out to be a professional baseball player, so he turned to a career in politics instead.

6. Though everyone today knows that President Franklin Roosevelt suffered from polio, the doctor he visited when he first experienced symptoms misdiagnosed him and subjected him to two weeks of deep massaging. This treatment unfortunately made the disease worse, and ultimately cost him the use of his legs. Had he been properly diagnosed, he may have received treatment that could have more positively influenced his health in the long run, and possibly even bought him a few more years to see the end of World War II and the resulting negotiations.

7. Prior to Archduke Franz Ferdinand’s assassination, one of his officers was injured in an assassination attempt. The Archduke decided to visit his officer in the hospital, but on the way there, his car took a wrong turn and gave the assassin the opportunity to kill the Archduke and his wife.

8. Unfortunately for the crew and passengers aboard the Titanic, one of the crew masters was replaced at the last minute before the ship began its voyage, and he forgot to hand over the key to the locker which held the binoculars to the new crew master. Had the crew had access to binoculars, it is possible they would have seen the iceberg in time to steer clear of it.

9. During World War II, the British Ambassador to Turkey’s butler was spying on the Allies because Turkey was considering entering the War on the side of the Axis powers. Being the butler, he had unfettered access to the Ambassador’s files, and he was able to uncover and copy top secret information, including the Allies’ plans for D-Day. However, when he turned the information over to the Germans, they thought him to be an unreliable spy. As a result, they disregarded the information, intelligence that could have changed the outcome of the war.

10. Marco Polo was imprisoned in a Genoan jail after the Venetian ship he was fighting on was captured during a trading war in 1298. His cell mate convinced him to document his travels and experiences in Asia, which the cell mate later published. The advice of the loquacious cell mate led to a wellspring of knowledge for Europe in the High Middle Ages.