The word(s) "fail" appears 18 time(s) in 18 verse(s) in Quran in Mohsin Khan translation.

(1) O you who believe! Take not as (your) Bitanah (advisors, consultants, protectors, helpers, friends) those outside your religion (pagans, Jews, Christians, and hypocrites) since they will not fail to do their best to corrupt you. They desire to harm you severely. Hatred has already appeared from their mouths, but what their breasts conceal is far worse. Indeed We have made plain to you the Ayat (proofs, evidence, verses) if you understand.

(2) "Wheresoever you may be, death will overtake you even if you are in fortresses built up strong and high!" And if some good reaches them, they say, "This is from Allah," but if some evil befalls them, they say, "This is from you (O Muhammad صلى الله عليه وسلم)." Say: "All things are from Allah," so what is wrong with these people that they fail to understand any word?

(3) (And remember) when you (the Muslim army) were on the near side of the valley, and they on the farther side, and the caravan on the ground lower than you. Even if you had made a mutual appointment to meet, you would certainly have failed in the appointment, but (you met) that Allah might accomplish a matter already ordained (in His Knowledge), so that those who were to be destroyed (for their rejecting the Faith) might be destroyed after a clear evidence, and those who were to live (i.e. believers) might live after a clear evidence. And surely, Allah is All-Hearer, All-Knower.

(4) Except those of the Mushrikun (see V.2:105) with whom you have a treaty, and who have not subsequently failed you in aught, nor have supported anyone against you. So fulfil their treaty to them for the end of their term. Surely Allah loves Al-Mattaqun (the pious - See V.2:2).

(5) So, when they despaired of him, they held a conference in private. The eldest among them said: "Know you not that your father did take an oath from you in Allah's Name, and before this you did fail in your duty with Yusuf (Joseph)? Therefore I will not leave this land until my father permits me, or Allah decides my case (by releasing Benjamin) and He is the Best of the judges.

(6) So think not that Allah will fail to keep His Promise to His Messengers. Certainly, Allah is All-Mighty, All-Able of Retribution.

(7) Each of those two gardens brought forth its produce, and failed not in the least therein, and We caused a river to gush forth in the midst of them.

(8) "Then verily, we can produce magic the like thereof; so appoint a meeting between us and you, which neither we nor you shall fail to keep, in an open place where both shall have a just and equal chance (and beholders could witness the competition)."

(9) Musa (Moses) said to them: "Woe unto you! Invent not a lie against Allah, lest He should destroy you completely by a torment. And surely, he who invents a lie (against Allah) will fail miserably."

(10) Musa (Moses) said: "Then go away! And verily, your (punishment) in this life will be that you will say: "Touch me not (i.e. you will live alone exiled away from mankind); and verily (for a future torment), you have a promise that will not fail. And look at your ilah (god) to which you have been devoted. We will certainly burn it, and scatter its particles in the sea."