Decisive
On the one hand, every program should be as simple as possible, but on the other hand, every program is characterized by the ability to comprehend different possibilities of acting, which allows it to react on different circumstances, such as different inputs.
This is true even in case that it is just a matter of becoming active or not, a simple question of yes or no, of on or off, 1 or 0.
Different possibilities and the involved moment of decision are decisive for even the smallest elements of programs. They are the base of every computational task.
Decision changes everything. The whole thing — and especially its relations to the parts. So that these become much more a matter of coordination than of addition.