John and Kathleen Bricker (defendants) leased a store in a mall from DVM Company (plaintiff). DVM obtained a percentage of sales from the Brickers and most other tenants in the mall. The lease permitted the Brickers to sell “Arizona Souvenirs” and stated that DVM’s consent was required prior to the Brickers’ use of the premises for any other purposes. Without DVM’s consent, the Brickers began selling T-shirts depicting movie and television characters and related slogans. DVM brought suit, claiming that these sales violated the lease. At trial, DVM sought to present evidence that the T-shirt sales affected the sales of other mall tenants. The trial court sustained the Brickers’ objection on this point. The trial court held that the T-shirt sales violated the lease, but that the violation was not so substantial so as to warrant forfeiture of the lease. The court of appeals affirmed. DVM appealed.