As early as in the case of People v. Oanis and Galanta, the Court has ruled that mistake of fact applies only when the mistake is committed without fault or carelessness: In support of the theory of non-liability by reasons of honest mistake of fact, appellants rely on the case of US. v. Ah Chong, 15 Phil., 488. The maxim is ignorantia facti excusat, but this applies only when the mistake is committed without fault or carelessness. In the Ah Chong case, defendant therein after having gone to bed was awakened by someone trying to open the door. He called out twice, "who is there," but received no answer. Fearing that the intruder was a robber, he leaped from his bed and called out again., "If you enter the room I will kill you." But at that precise moment, he was struck by a chair which had been placed against the door and believing that he was then being attacked, he seized a kitchen knife and struck and fatally wounded the intruder who turned out to be his room-mate. 

A common illustration of innocent mistake of fact is the case of a man who was marked as a footpad at night and in a lonely road held up a friend in a spirit of mischief, and with leveled, pistol demanded his money or life. He was killed by his friend under the mistaken belief that the attack was real, that the pistol leveled at his head was loaded and that his life and property were in imminent danger at the hands of the aggressor. In these instances, there is an innocent mistake of fact committed without any fault or carelessness because the accused, having no time or opportunity to make a further inquiry, and being pressed by circumstances to act immediately, had no alternative but to take the facts as they then appeared to him, and such facts justified his act of killing (People v. Gervero, G.R. No. 206725, July 11, 2018).