Curve of Acceleration

While this curve of acceleration is the "law of the key" for all singing or good tone, it applies equally in the production of the softest pp.
Thus, for real ppp you must in pianissimo slowly feel your way to that point in key-descent where you can feel the hopper beginning to slide from underneath the hammer "button". You can feel this as a slight impediment, and from there only may you add the true tone-producing impulse.
Playing, in fact, is exaggerated singing-tone so far as the method of production is concerned.
Unless you master this technique, you can never command a true ppp and unless you can command that, your whole range of tone is much narrowed.
From a sound and dynamics perspective, realize that your fortes are truly fortes only in proportion that your pianos are truly pianos. You can therefore only produce the effect of a correct forte by being able to produce the softest sound.

How does a pianist achieve ppp in piano playing? To achieve ppp (pianississimo) in piano playing, a pianist must use a delicate touch on the keys with their fingers. This means that the pianist must play with a very soft touch and use minimal force when striking the keys. Additionally, the pianist may need to adjust their body position to produce the desired sound. For example, they may need to sit closer to the keyboard or lower their hands to achieve a softer touch.
Furthermore, the pianist may also need to control their breathing and use their diaphragm to support their playing. This is because the amount of air pressure the pianist uses when playing can affect the volume and tone of the notes produced.
Overall, achieving ppp requires a combination of physical and technical skills, as well as sensitivity and control in the execution of the music. With practice and attention to detail, a pianist can develop the ability to play at very low volumes while still maintaining clarity, expression, and musicality.

ppp which stands for pianississimo and meaning "very very quiet". To gain this skill of real ppp playing perform the following:
Take a chord of three or four notes, and with fingers firmly fixed against the key-surfaces, move those keys down only so far as the hopper impediment, and let them rise again.
Repeat this a number of times, until you feel confident with it, then follow this movement to the hopper by the very slight additional movement that will swing the hammer to the string, and will thus sound the notes really at their very softest. This is an excellent way of realizing what is meant by "key-attention".