Jesus Christ identified four tendencies that undermine faith in statements where He chided others with the phrase "O you of little faith." These are:

Worry

Jesus said God would take care of our needs, cautioning: "Do not worry . . . Now if God so clothes the grass of the field [splendidly], which today is, and tomorrow is thrown into the oven, will He not much more cloth you, O you of little faith? Therefore do not worry . . . But seek first the kingdom of God and His righteousness, and all these things shall be added to you" (Matthew 6:25-33 Matthew 6:25-33 [25] Therefore I say to you, Take no thought for your life, what you shall eat, or what you shall drink; nor yet for your body, what you shall put on. Is not the life more than meat, and the body than raiment? [26] Behold the fowls of the air: for they sow not, neither do they reap, nor gather into barns; yet your heavenly Father feeds them. Are you not much better than they? [27] Which of you by taking thought can add one cubit to his stature? [28] And why take you thought for raiment? Consider the lilies of the field, how they grow; they toil not, neither do they spin: [29] And yet I say to you, That even Solomon in all his glory was not arrayed like one of these. [30] Why, if God so clothe the grass of the field, which to day is, and to morrow is cast into the oven, shall he not much more clothe you, O you of little faith? [31] Therefore take no thought, saying, What shall we eat? or, What shall we drink? or, Wherewithal shall we be clothed? [32] (For after all these things do the Gentiles seek:) for your heavenly Father knows that you have need of all these things. [33] But seek you first the kingdom of God, and his righteousness; and all these things shall be added to you.
American King James Version×).

Fear

While on a boat in the middle of a storm, the disciples woke Jesus and pleaded that He save them from drowning. He answered, "Why are you fearful, O you of little faith?" Then He rebuked the sea and it immediately grew calm (Matthew 8:23-26 Matthew 8:23-26 [23] And when he was entered into a ship, his disciples followed him. [24] And, behold, there arose a great tempest in the sea, so that the ship was covered with the waves: but he was asleep. [25] And his disciples came to him, and awoke him, saying, Lord, save us: we perish. [26] And he said to them, Why are you fearful, O you of little faith? Then he arose, and rebuked the winds and the sea; and there was a great calm.
American King James Version×).

Doubt

Peter saw Jesus walking on the water of the Sea of Galilee and asked if he could do the same. Jesus invited him to join Him, and Peter, too, began walking on the water. "But when he saw that the wind was boisterous, he was afraid" and began to sink (Matthew 14:30 Matthew 14:30But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me.
American King James Version×). Christ "stretched out His hand and caught him, and said to him, 'O you of little faith, why did you doubt?'" (Matthew 14:31 Matthew 14:31And immediately Jesus stretched forth his hand, and caught him, and said to him, O you of little faith, why did you doubt?
American King James Version×).

Human reasoning without spiritual understanding

Jesus warned His disciples, "Take heed and beware of the leaven of the Pharisees and the Sadducees" (Matthew 16:6 Matthew 16:6Then Jesus said to them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.
American King James Version×). He was cautioning them against the wrong teachings of these religious leaders (Matthew 16:12 Matthew 16:12Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees.
American King James Version×), but the disciples initially thought He was talking about the physical leavening of bread since they had not brought any bread with them (Matthew 16:7 Matthew 16:7And they reasoned among themselves, saying, It is because we have taken no bread.
American King James Version×). Jesus responded, "O you of little faith, why do you reason among yourselves because you have brought no bread?" (Matthew 16:8 Matthew 16:8Which when Jesus perceived, he said to them, O you of little faith, why reason you among yourselves, because you have brought no bread?
American King James Version×). He then said that they wouldn't have missed His point if they'd kept in mind that He could miraculously provide physical bread if there was a need, having done so to feed thousands on two occasions (Matthew 16:9-11 Matthew 16:9-11 [9] Do you not yet understand, neither remember the five loaves of the five thousand, and how many baskets you took up? [10] Neither the seven loaves of the four thousand, and how many baskets you took up? [11] How is it that you do not understand that I spoke it not to you concerning bread, that you should beware of the leaven of the Pharisees and of the Sadducees?
American King James Version×).