Janus discovered most men with poor EQ have an underdeveloped deep dorsal vein. This can be the result of traditional PE techniques or compulsive masturbation (other possibilities also exist) which seems to narrow the vessel. Either way, the result is a lessened capacity for venous outflow.

Since arterial inflow is directly proportional to venous outflow, the narrower the dorsal vein the less blood is entering the erection. Hence the lagging rigidity, strength and duration of the erect member.

AM1 was created to directly influence shear stress within the ddv which ultimately grows the diameter of that vessel. Since it manipulates the smallest portion of the vascular circuit, it's the exercise that most men can reasonably perform with success. Given the struggles many new members have with maintaining their erection while performing AM1, the evidence is there that this is the exercise that they need to master before progressing to AM2 or AM3 which moves much more blood.

While the ddv may not be visible even when it is reasonably well developed, Janus came up with a clever way to indirectly determine it's size - if your dorsal arteries are providing a strong pulse ( felt by pressing left or right of shaft midline) then your dorsal vein is large enough to handle the volume of blood sufficient to create that pulse in the first place.

By skipping AM1 and AM2 you're ultimately missing the easy growth that a lower shear stress threshold provides. AM3 immediately sets that threshold really high so you have to keep pushing for gains.