It's a routine move called a "go-around". It usually happens when there is something still on the runway - a plane that hasn't completely cleared, sometimes an airport vehicle, or even an animal that wanders in. Either the pilot or the controller in the tower can call for a go-around.

Less often it's something in the plane landing that is amiss - if a plane it at the wrong speed or altitude for landing, or if flaps or gear aren't set right, a bad indicator light. or some other switch or dial that doesn't read right, the plane may go around. Maybe the wind shifted or there was an unexpected gust at critical time.

Finally, if the pilot just doesn't feel "right" about the landing they will go around and try again