If it's below the threshold value, that will not take place. That's exactly what we mean by all or nothing. It either takes place or it doesn't. Now, this also means that no matter how high the stimulus actually is, the amplitude or the magnitude of this wave will be exactly the same. So even if the stimulus is very, very high, this value, the height of the curve, will not change. So by increasing the stimulus, we are not affecting the amplitude of our action potential.