Jesus spoke of the man who built his house on the sand:
Every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand: 27 And the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell: and great was the fall of it.
Faith comes by hearing the Word of God, Christ, Romans 10:17. The "house" here represents a man's faith in Christ, while the "foundation," (or lack thereof in this case), represents his works of obedience to Christ. A man's faith in Christ stands upon his obedience to Christ. But if a man's obedience to Christ is lacking, eventually his faith in Christ will come crashing down. Judas Iscariot set the example for this when, although appearing to men no different from the other apostles, he was secretly disobedient and in the end his faith suddenly collapsed with a great fall:
Now the names of the twelve apostles are these; The first, Simon, who is called Peter, and Andrew his brother; James the son of Zebedee, and John his brother; 3 Philip, and Bartholomew; Thomas, and Matthew the publican; James the son of Alphaeus, and Lebbaeus, whose surname was Thaddaeus; 4 Simon the Canaanite, and Judas Iscariot, ...
John 6:63-71 Jesus taught,
It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life. 64 But there are some of you that believe not. (For Jesus knew from the beginning who they were that believed not, and who should betray him). 65 And he said, Therefore said I unto you, that no man can come unto me, except it were given unto him of my Father. 66 From that time many of his disciples went back, and walked no more with him. 67 Then said Jesus unto the twelve, Will ye also go away? 68 Then Simon Peter answered him, Lord, to whom shall we go? thou hast the words of eternal life. 69 And we believe and are sure that thou art that Christ, the Son of the living God. 70 Jesus answered them, Have not I chosen you twelve, and one of you is a devil? 71 (He spake of Judas Iscariot the son of Simon: for he it was that should betray him, being one of the twelve).
Then Jesus six days before the passover came to Bethany, where Lazarus was which had been dead, whom he raised from the dead. 2 There they made him a supper; and Martha served: but Lazarus was one of them that sat at the table with him. 3 Then took Mary a pound of ointment of spikenard, very costly, and anointed the feet of Jesus, and wiped his feet with her hair: and the house was filled with the odour of the ointment. 4 Then saith one of his disciples, Judas Iscariot, Simon's son, which should betray him, 5 Why was not this ointment sold for three hundred pence, and given to the poor? 6 This he said, not that he cared for the poor; but because he was a thief, and had the bag, and bare what was put therein. 7 Then said Jesus, Let her alone: against the day of my burying hath she kept this.
Now the feast of unleavened bread drew nigh, which is called the Passover. 2 And the chief priests and scribes sought how they might kill him [Jesus]; for they feared the people. 3 Then entered Satan into Judas surnamed Iscariot, being of the number of the twelve. 4 And he went his way, and communed with the chief priests and captains, how he might betray him unto them. 5 And they were glad, and covenanted to give him money. 6 And he promised, and sought opportunity to betray him unto them in the absence of the multitude. 7 Then came the day of unleavened bread, when the passover must be killed.
John 13: verses showing Judas Iscariot forming thought to betray Jesus
John 18: verses showing Judas Iscariot betraying Jesus
Then Judas, which had betrayed him, when he saw that he was condemned, repented himself, and brought again the thirty pieces of silver to the chief priests and elders, 4 Saying, I have sinned in that I have betrayed the innocent blood. And they said, What is that to us? see thou to that. 5 And he cast down the pieces of silver in the temple, and departed, and went and hanged himself.