Here's why:
* Card Text is Binding: The text on a Yu-Gi-Oh! card is the rule for that card. If a card states "Discard 1 card," it means you *must* discard a card to play it.
* Conditions Must Be Met: In order to activate a card effect or play a card, all the stated conditions must be met. If you cannot fulfill the "discard" condition, the card cannot be activated or played.
Example:
Let's say you have a card that says: "Discard 1 card. Draw 1 card." If you have no cards in your hand, you cannot play this card because you cannot fulfill the discard requirement.
Exceptions:
While there are a few exceptions to this rule, they are rare and specific. Some examples might include:
* Cards that allow you to discard from your deck: Some cards allow you to discard cards directly from your deck instead of your hand.
* Cards that allow you to discard other things: Some cards might let you discard something other than cards from your hand, like tokens or other cards on the field.
In Summary:
Generally speaking, if a card requires you to discard from your hand, you must have a card in your hand to play it.