After Shimon and Levi killed all the men of Shchem, Yaakov Avinu was afraid and he said, “I will be annihilated.” Why is this not considered “opening one’s mouth to the Satan,” as Yaakov was saying a curse on himself?
You are asking a very interesting question, and I don’t have a good answer al pi pshat. I did however see a fascinating idea on this in a sefer Nefesh Dovid, al pi remez. He asks the question, how did Yackov say such a thing in the first place, it wasn’t true, because the local people didn’t kill him and his family, so how could the torah write this? He answers this with what is written in the sefer Amundeha Shiva in the name of the Arizal. That Shimon and Levi killed out 24,000 people in Shechem, however since they did bris milah, there was need for a kapara, and these 24,000 people came down in a gilgul in shevet Shimon (who killed Shechem etc.), however since they were killed because of an aveiro of zenus, there was still a need for a kapara. Additionally, Yackov was held accountable in a way for this because he didn’t stop them, therefore Yackov Came down again in the form of R’ Akiva, (the posuk אבי”ר יעק”ב is the same letters as רבי עקיבא, also יעקב and עקיבא have the same letters, but יעקב is missing an א, and this that R’ Akiva was killed, and his neshoma went out at אחד, was for the א’ of עקיבא.) This is what Yackov told the brothers, you made me “dirty” that now I will have to come back to this world, and because of this I and my family, (my disciples, like Beis Shamai, Beis Hillel, means the yeshiva of) will eventually get killed. He says that this is also what he said, מתי מספר, that they will get killed “when they count”, meaning during the days of counting, (the vowel under the Mem would then be changed from a pasach to sound like matay.) According to this, Yackov was actually saying a prophesy, that because of what they, this is what they caused and this will eventually happen.