R. Hiyya b. Abba was asked: What if one forgot a pot on the stove and [thus] cooked it on the Sabbath? He was silent and said nothing to them [his questioners]. The next day he went out and lectured to them: “If one cooks [food] on the Sabbath unwittingly, he may eat [it]; if deliberately, he may not eat [it]; and there is no difference.”
The intention of the person matters. We have learned that you cannot cook or even leave a dish on a hot wood or charcoal fed stove. But what if a pot is accidently left on after the Sabbath begins, must the food be forbidden? Seemingly not – if there is no intention to break the law, it is reasonable to allow it.
But things don’t always stay that way.
R. Judah b. Samuel said in the name of R. Abba in the name of R. Kahana in Rab's name: At first it was ruled: One who cooks [food] on the Sabbath unwittingly, may eat it, if deliberately, he may not eat. The same applies to one who forgets.
But when those who intentionally left [it there] grew numerous, and they pleaded, "We had forgotten [it on the stove]," they [the Sages] retraced their steps and penalized him who forgot.
It seems once a loophole is found, it will be exploited. So the law becomes ever more restrictive.