We present a detailed analysis of size-down trajectories of the "Shrinking Hot Giant" road of fullerene formation, revealed before by our quantum chemical molecular dynamics simulations. It is found that shrinkage of giant fullerenes occurs in two stages, fall-off and pop-out stage, respectively, and that it is an irreversible process occurring naturally at high temperatures. The driving force behind the energetically unfavorable C2 evaporation is the increase in entropy and pi-conjugation stabilization of the increasingly more spherical fullerene cages. A comparison of the theoretical results with existing experimental data shows the importance of annealing for the synthesis of smaller (C60, C70) fullerenes.