Landing is not a decision that you make once and commit to carry out come what may. It is subject to change if circumstances warrant. Consider the “go-around,” which is essentially an aborted landing. (It could also be said that every landing is an aborted go-around.)

In a proper go-around, the pilot follows established procedures to safely discontinue the descent, stabilize the aircraft, and climb back up for another try. You should go around if another airplane, a person, or an animal enters the runway that you intend to land on. Less obvious but equally valid reasons to try, try again include: being significantly off the runway centerline, too high or too low, too fast or too slow. If your airspeed, altitude, heading, or pitch are changing constantly, not settled on target, that's called an unstable approach, which is an excellent reason to go around. You should also break off any approach that just doesn’t feel right.

There are other decisions pilots make that are subject to revision, starting with the very first significant decision of the day, whether to fly at all. When making this “go/no-go” decision, pilots analyze known hazards during preflight preparation and evaluate the risk/benefit equation of the flight. It’s similar to a go-around, in that when you opt “no-go,” you are really saying, “I’ll go another time.”

But there’s one other time when you can revise your decision to proceed with a flight that doesn’t get quite as much attention, and that’s the aborted takeoff. Like it sounds, it’s a takeoff that has started, but then is stopped. There’s a procedure that varies by aircraft , but it basically boils down to: throttle to idle; brakes as required; don’t worry about the radio calls until the aircraft has slowed down to a nice, slow taxi pace.

Do I dare
Disturb the universe?
In a minute there is time
For decisions and revisions which a minute will reverse.

—T.S. Eliot, from “The Love Song of J. Alfred Prufrock”

The important thing here is your mindset. Applying full throttle does not commit you to flight. In a small piston airplane using a typical 5,000-foot runway, a takeoff may be aborted even after lifting off—if there is enough runway to set down again safely.

Why would you abort a takeoff? For any of the same reasons you might abort a landing: Someone or something enters the runway ahead of you, you drift significantly off centerline, your takeoff run is unstable for any reason, or if it just doesn’t feel right. Also, any indication that the powerplant is not working to its potential, such as excessive vibration, a strong odor, or instrument indications, is another fine reason to remain within the runway limits.

Flying is full of decisions. Being alert to changing circumstances and willing to embrace revision are among the qualities that define the "command" element of PIC, and make for a safe and successful pilot.