The basic model for projectiles necessarily needed to make many assumptions. However, this situation is almost impossible to obtain in the real world. Wind, air resistance, and physical limitations all affect the real path of a missile.
Physical obstructions are also absent from the simple model.
In order to accurately portray a trajectory in real life, these factors must be taken into account. The inclusion of these variables makes for a more realistic computational model. The real world factors that are added all deal with forces acting on the missile. Wind sways a projectile's motion by pushing it from its intended path. The physical limitations are necessary to prevent obtaining absurd results.