There is a phrase that many children and even some adults hear on a regular basis. It’s something that every parent says generation after generation. Because I said so! An annoyingly common phrase is when the people in charge become upset at incessant demands. Children will demand and demand and demand. Sometimes parents will give in, and just give the child what they want but that fails to teach the child any manners. But saying “Because I said so!” to the child will frustrate them just as much as the parent. It just gives a general statement of why the parent is saying no.
Urban Dictionary defines the phrase as an imperious reply that an authority figure, most often a parent, impatiently tells someone under his/her care when he does not wish to admit that there is literally no good/valid reason why said dependent should have to comply with the directive, but the authority figure doesn't want to admit it.
There is a lot of psychology involved with using the common phrase. It can cause a negative impact on a child’s mental growth. However, there can be other ways of getting your point across. Explaining the reasoning behind a decision and the way that you came to the decision doesn’t always mean that the decision is up for negotiation. When a decision is reached, it can sometimes be disappointing to the child, he or she will almost certainly ask why. Usually, this doesn’t stem from belligerence or disrespect, though the child may be genuinely disappointed or upset. For the most part, when children ask why, it’s because they genuinely don’t see the harm, danger, or inconvenience of their request. Be respectful of the child’s question and share your own reasons, concerns and doubts. Maybe the child will be disappointed but it's better to explain your reasons than to not give any at all.
Parents everywhere may be disappointed because using that phrase is not the norm anymore. They were probably annoyed by the phrase as children and proceeded to use it on their own children. It can be difficult to use something new but the world is always evolving in the ways we speak to our children.