Lift is a force, lift works against weight. Lift is created mostly by the wings of a bird or plane. Lift makes objects come off the ground. Weight is the force that pulls planes down to the ground. Drag is a force. Drag is used to slow the plane down so it is able to land. Thrust is used to overcome the drag of an airplane, it is a force that moves an aircraft through the air.
Planes fly because of lift and thrust. Lift gets the plane off the ground and thrust keeps an aircraft moving through the air. Drag is the force that slows the plan down, drag is important when the plane is landing. Drag slows the plane down when the plane is about to hit the ground. For planes weight is always pointed to the centre of the earth, weight is important for landing because it holds the plane to the ground.
In conclusion, it is clear that planes need the four forces in order to fly. It's clear that humans can't fly because gravity is pulling them down, as they don't have enough lift and thrust to overcome gravity and their heavy bodies.