410.5. Some triggered abilities’ effects are optional (they contain “may,” as in “At the beginning of
your upkeep, you may draw a card”). These abilities go on the stack when they trigger
, regardless of
whether their controller intends to exercise the ability’s option or not. The choice is made when the
ability resolves. Likewise, triggered abilities that have an effect “unless” something is true or a
player chooses to do something will go on the stack normally; the “unless” part of the ability is
dealt with when the ability resolves.