According to Isaiah, people who say good things about themselves or promise something should do so by trusting in God, who always tells the truth. This is because God will make past problems disappear and not remember them anymore.
Isaiah 65:16: That he who blesseth himself in the earth shall bless himself in the God of truth; and he that sweareth in the earth shall swear by the God of truth; because the former troubles are forgotten, and because they are hid from mine eyes.
James states that God cannot be tempted with evil, neither does He tempt anyone, which seems to contradict the notion in Isaiah 65:16 where God is considered as the ultimate authority over both blessings and curses.
James 1:13: Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man: [evil: or, evils]