In general, all game effects are mandatory. If you cannot fully resolve an effect, you must resolve as much as you can. Effects after the arrow symbol are only resolved if the condition before the arrow is completely fulfilled. If it is, the effect after the arrow must be resolved.

There are three exceptions where effects are optional: 

• May: Effects that say you “may” do something are optional. 
• Activating Effects: Using an activated effect is optional. (See: Activated Effects.)