The "no tiara" rule primarily applies to unmarried girls and royal ladies under 18. Traditionally, tiaras are associated with brides on their wedding day or married women, symbolizing the transition from innocence to love. Tiaras are typically lifetime loans, becoming exclusive to the wearer for their entire life. The Queen may choose or offer a selection of tiaras for special occasions like weddings, though the wearer's input on style and size is uncertain.