Presumption

146. After considering pride in itself, it remains for us to observe its effects, and especially eight of the more common and familiar vices which it produces, which are presumption, ambition, envy, vainglory, boastfulness, hypocrisy, disobedience and discord. Let us examine them with St. Thomas.
Presumption is a vice by which we esteem ourselves able to achieve things beyond our strength, forgetful of the necessity of Divine help. The sinner is guilty of presumption when he believes that he can be converted to God whenever he likes and chooses, as if conversion were the work of his own free-will alone, and living ill yet trusts to make a good death; when he sins and goes on sinning, relying upon obtaining ultimate forgiveness; when he believes that he can of himself, and without the help of grace, both withstand temptation, avoid sin and observe the commandments of God, or else that he can make some supernatural act of faith, hope, charity or contrition, or perform some meritorious act towards his eternal welfare and save himself by persevering in well-doing.
All this is beyond our own strength, and to think that we can do these things without the special help of God, and without being willing to ask this help of God, is a sin of presumption-----a grave sin of that pride by which we believe that we possess a virtue when we have it not: "O wicked presumption," says Holy Writ, "whence camest thou?" [Ecclus. xxxvii, 3] And Saint Gregory, explaining what that sin was which Job called "great iniquity," [Job cxxxi, 28] affirmed that it was presumption, which is an insult to the author of all grace, "by which a man takes all the credit of a good work to himself." [Lib. xxii, Mor., cap. x]