"Minimum power, maximum efficiency..."
Shuji Maruyama Sensei
Once we understand how to generate Ki power and make a connection to our uke (03b Ki: Transferring Power) we can use the principle of the circle, triangle and square to apply the minimum power correctly to uke for maximum effect.
With the principle of the circle we move around uke to find the safe entry point. We use the principle of the triangle to pierce with our focused power. And using the principle of the square, we align our body in the strongest position at uke's weakest point.
In general (the Yoshinkan school's kihon or basics teach this really well) we want to apply our power parallel to the narrowest base of the rectangle formed by uke's feet. If applied equally uke is unable to move their feet, either to counter or to step forward/back to a better position.
Watch the body positioning and timing of Thambu Sensei (while the Yoshinkan school applies more power than our school the principles remain the same):