This is a psychological shadow.
This is fear!
"When I first crossed swords with you, an unexpected strike hit you at your weakest point, allowing me to defeat you."
"After that, I was always able to quickly find your weaknesses and beat you."
After over a month of practice, Lu Anya began to learn how to hide her own weaknesses and discover those of her opponent.
This allowed Lu Anya's strength to increase rapidly, to the point where even her senior sister, due to the huge gap in attributes, could no longer spar with her.
"And today, when I sparred with you, there was still a huge gap between our strengths."
The senior sister compared herself and Lu Anya to two armies, "It's like two forces in battle, mine of 50,000 against your 100,000, your troop number is twice mine."
But troops are just troops, they don't represent everything!
A capable general leading new recruits can still defeat a novice commanding veterans.