Everything Being Handed Out on a Silver Platter
Being an only child may lead to excessive pampering, which may hamper your progress to become more independent and responsible. For example, demanding and getting the latest video game only because it was owned by a peer. The damage done by this kind of pampering is felt in the long run, as you may always turn to your parents for whatever your needs may be.
Not Having a Sibling to Socialize With
Playing with those toys all by yourself could be delightful. But, at the end of the day, sharing what you have with others leads to more happiness. Having a sibling, older or smaller, means you have someone close to share your thoughts and memories with. Sometimes, being an only child could be lonely.
Being in the Continuous Spotlight of Parental Supervision
Parents may put a lot of pressure to perform well academically as well as socially, as you are the only one they can pin their hopes upon. While this pressure may not be present directly, the child feels it through subliminal messages when exams are nearby, or when there is a social gathering. Parents tend to be over-protective of a single child, and may overwhelm them with attention.