Plain English Meaning
The faster you try to do something, the more mistakes you tend to make. The more careful you try to be, the slower you go. You usually can't push both at the same time, especially while still learning.
Full Definition
A learning and performance principle stating that as a person tries to perform a task faster, accuracy tends to decrease, and as they try to perform it more accurately, speed tends to decrease. In flight training, it describes the natural tension between completing a maneuver or procedure quickly and completing it correctly.
Context Anchor
Seen in aviation instruction and human factors discussions, especially when explaining why pilots make errors during busy or time-pressured cockpit .