What must players do if they realize they have an insufficient number of lands in their deck?

If players discover they have an insufficient number of lands in their deck, the appropriate course of action is to inform a judge immediately. This is essential because having an inadequate number of lands violates the deck construction rules and can affect the fairness of the match. By alerting a judge, players ensure that the situation can be assessed properly and that any necessary adjustments can be made according to tournament rules.

Taking any other action, such as continuing to play with the incorrect deck or making changes without notifying a judge, could lead to penalties or unfair advantages during the match. Hence, the rule emphasizes the importance of maintaining honest and fair play by involving a judge in such scenarios.