Doraemon Tram

Doraemon’s story plot is based on a real-life incidence. The story has received so much of sarcastic criticism that it has now become a controversy. The real emotional story of the series Doraemon is that “Nobita” was suffering from Schizophrenia. It is a disorder in which a person has less ability to think, feel and behave clearly. Moreover, his mental controlling power diminishes. Nobita was also abused and bullied in his school by his classmates because he suffered from this mental condition. His friends left him fearing that one-day Nobita can provide harm to them and he became lonely. Due to the disease and loneliness, he felt mediocre, abandoned and stressed out.

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His medical condition forced him to imagine the character of Doraemon to help him in every possible way. Later on, making Doraemon Nobita’s best (imaginary) friend. At 16, he started medical counseling for the treatment of his disease. The doctor then told him that Doraemon does not exist. It is just a mere imagination of his unconscious mind over which he needs to put control. 
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This isn't cannon to Doraemon lore. This is just a dark fan theory that is commonly spread on the internet. Many times in the show you see other characters interacting with Doraemon in the past and future, as well as the main lore mainly mentioning Nobita's decedent's who know/sent Doraemon back in time.