Calter took his first step on the stairs and he can suddenly feel pressure bearing down on his body and soul. But since it was just the first step, the pressure is too weak to cause any harm to him
Calter continued and took his second, third, fourth, fifth, and so on steps. The more steps he took, the stronger the pressure becomes. Even then, Calter didn't lose his composure and focuses on the task in front of him
Panicking won't do him any good. In fact, it will just make his will weaker and the chances of him failing and dying would be higher if that happens
Calter didn't know how much time has passed and he doesn't care. The only thing in his mind at that time was ascending this stair
Even after Calter took his hundredth step, the end of the stairs is still far from him. He judges there he only took one-tenth of the overall steps. Meaning that this stair might have a thousand steps