What are the sins against hope? The sins against hope are presumption and despair.
When does a person sin by presumption? A person sins by presumption when he trusts that he can be saved by his own efforts without God's help, or by God's help without his own efforts.
Nay I do not even judge my own self. For I have nothing on my conscience, yet I am not thereby justified. (I Corinthians 4:4)
When does a person sin by despair? A person sins by despair when he deliberately refuses to trust that God will give him the necessary help to save his soul.
May no temptation take hold of you but such as man is equal to. God is faithful and will not permit you to be tempted beyond your strength, but with the temptation will also give you a way out that you may be able to bear it. (I Corinthians 10:13)
Further reading: CCC 2090-2092