After the two beautiful talks given by Giulio and Alioscia, who respectively introduced to us the very board worlds of non-local quantum games and quantum irreversibility, I would like to lead a discussion on the adiabatic theorem, which is covered in almost all elementary quantum mechanics courses. In fact, the adiabatic theorem was first proved by Born and Fock in 1928, i.e., at the dawn of quantum mechanics. Its applications cover a wide range of areas in physics and chemistry. The study of the adiabatic theorem is still a very active field of research. In particular, the quest for finding a "useable" indicator for quantum adiabaticity is still not finished. Previously, it was believed that the so-called quantitative condition is a sufficient condition for ensuring quantum adiabaticity. However, it was disproved by counter examples. On the other hand, the question of the necessity of the quantitative condition has been controversial. In this talk, after laying out the background story, I will present a new result that contains an exact expression which connects directly the quantitative condition with transition amplitudes. This expression gives a transparent picture why the quantitative condition fails to reveal quantum adiabaticity.