The ego is the driver making the decisions. It decides between the devil (the id) and the angel (the super-ego) on either shoulder (yes, all those cartoons you've ever seen are partly true). We have voices in our mind, and it's up to the ego to decide which one to fulfill. Its goal is to satisfy the id in some way while also attending to the super-ego.

When an airplane leaves from one city to the next, it has a plan. Its plan is called a flight plan. It's a massive action plan that involves speed, altitude, direction of travel and many other facets. But what happens when there's turbulence or air-traffic congestion or it needs to change course for some other reason? The plane changes its plan. But it doesn't change its goal of where it's going. Create and follow a plan, and don't be afraid to change it if you see something isn't working.