I agree, not scientific. The objective is to manipulate training volume and intensity to ensure constant progression. You must apply the MINIMUM amount to achieve a physical adaptation, then up it just enough to get a further improvement and so-on.
If you set the bar too close to ceiling too early on, then you'll soon have no where to go! The idea is to keep progressing continuously, not plateau and get stuck.
I've explained more on this in a previous short article:
heatrick.com/2012/07/27/training-dose/