Contradiction with Proverbs 4:7
Mark 8:17 questions understanding, while Proverbs 4:7 emphasizes obtaining wisdom and understanding as the principal thing.
Proverbs 4:7: Wisdom [is] the principal thing; [therefore] get wisdom: and with all thy getting get understanding.
Contradiction with 1 Corinthians 2:14
Mark 8:17 questions why the disciples don't perceive or understand, while 1 Corinthians 2:14 explains that spiritual truths are foolishness to the natural man who cannot understand them.
1 Corinthians 2:14: But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know [them], because they are spiritually discerned.
Contradiction with Hebrews 5:11
Mark 8:17 questions the disciples' lack of understanding, whereas Hebrews 5:11 mentions believers being dull of hearing, suggesting difficulty in understanding.
Hebrews 5:11: Of whom we have many things to say, and hard to be uttered, seeing ye are dull of hearing.
Contradiction with John 16:12
Mark 8:17 questions understanding, whereas John 16:12 implies there is more that cannot yet be understood.
John 16:12: I have yet many things to say unto you, but ye cannot bear them now.
Contradiction with Matthew 13:13
Mark 8:17 highlights lack of understanding, whereas Matthew 13:13 explains that speaking in parables leads to hearing but not understanding.
Matthew 13:13: Therefore speak I to them in parables: because they seeing see not; and hearing they hear not, neither do they understand.
Contradiction with 2 Timothy 3:7
Mark 8:17 questions perception and understanding, whereas 2 Timothy 3:7 describes individuals ever learning but never able to come to the knowledge of the truth.
2 Timothy 3:7: Ever learning, and never able to come to the knowledge of the truth.