The Gospel of Mark is quite short but is built around grave implausibility.
Here is a list of every instance in the Gospel of Mark where the disciples of Jesus and by extension others are explicitly shown to be confused, blind to spiritual truth, or in need of private explanation and correction even for things that should be obvious.
The Parable of the Sower Mark 4:10–20 explains itself. The disciples pull Jesus aside in private because they don't understand the story. Unsurprisingly Jesus rebukes them ("Do you not understand this parable? How then will you understand any...?") before explaining it.
It is supposed that Jesus in reality did not explain to the disciples - the Church had the stories and started putting interpretations on them.
Mark explicitly notes that Jesus never spoke to the public without a parable, but "explained everything in private to his own disciples." This does not ring true. The people would have demanded an explanation and crowds do not gather to listen to stories that hide a point and won't give it.
There is Mark 7:17–23. After telling a crowd that external things cannot make a person unclean, the disciples admit their confusion, prompting Jesus to ask, "Are you also so dull?" before explaining it plainly.
Regarding Mark 10:10–12. After debating the Pharisees publicly about divorce, Mark notes that "in the house the disciples asked him again about this matter." Jesus then gives them a private, stricter clarification.
There is the camel and needle image to illustrate how the rich can't enter Heaven unless God who can do the impossible makes it possible. Mark 10:23–27. When Jesus tells the crowd it is practically impossible for the rich to enter heaven, the disciples are "exceedingly astonished" and argue until Jesus explains God's perspective to them in private.
There is a huge mistake in that story. Jesus publicly says the rich cannot be helped towards God. Then in private he says only God can help them for nothing is impossible with God. You may argue that Jesus in fact didn't want the rich to know that. So what is the gospel revealing it for? And it does not fit how Judaism did have a doctrine of divine grace where God lifts people out of the depths when they repent and ask. It was the whole point of the baptism of John. We wonder if the Mark gospel was meant for public consumption at all. It probably was not as nearly everybody was illiterate. It is more likely that Jesus was indeed a doom goblin and never held any hope out for the rich.
In Mark 12, we are told Jesus then began to speak to them in parables: “A man planted a
vineyard. He put a wall around it, dug a pit for the winepress and built a
watchtower. Then he rented the vineyard to some farmers and moved to another
place. 2 At harvest time he sent a servant to the tenants to collect from them
some of the fruit of the vineyard. 3 But they seized him, beat him and sent
him away empty-handed. 4 Then he sent another servant to them; they struck
this man on the head and treated him shamefully. 5 He sent still another, and
that one they killed. He sent many others; some of them they beat, others they
killed. 6 “He had one left to send, a son, whom he loved. He sent him
last of all, saying, ‘They will respect my son.’ 7 “But the tenants
said to one another, ‘This is the heir. Come, let’s kill him, and the
inheritance will be ours.’ 8 So they took him and killed him, and threw him
out of the vineyard. 9 “What then will the owner of the vineyard do? He
will come and kill those tenants and give the vineyard to others. 10 Haven’t
you read this passage of Scripture:
“‘The stone the builders rejected
has become the cornerstone;
11 the Lord has done this,
and it is
marvelous in our eyes?”
12 Then the chief priests, the teachers of
the law and the elders looked for a way to arrest him because they knew he had
spoken the parable against them. But they were afraid of the crowd; so they
left him and went away."
There were ways and means of getting him out of the way. At least the story says the meaning was obvious.
There is the end times discourse Jesus cobbled together from Old Testament ramblings. The forged prophecies of the book of Daniel are mistaken as authentic by this Jesus who can be trusted with the future despite not getting the past right. Read Mark 13:3–4. After Jesus publicly states the Temple will be destroyed, Peter, James, John, and Andrew pull him aside "privately" on the Mount of Olives to ask what he meant, prompting a long secret discourse.
Read Mark 4:35–41. After Jesus calms a raging sea, the disciples panic in terror and confusion, asking each other, "Who then is this, that even the wind and the sea obey him?
Jesus supposedly miraculously supplied loaves and fishes.
Mark 6:51–52: When Jesus walks on the lake, the disciples scream in terror. Mark explicitly blames their confusion on spiritual blindness: "For they had not understood about the loaves, but their hearts were hardened." The message here is that they should have been fearless. Really? Does it make sense that if you see a person feeding a multitude with a little food that you would be surprised at him walking on water?
In Mark 8:14–21, Jesus warns them to watch out for the "yeast of the Pharisees." The disciples completely misunderstand, thinking he is mad because they forgot to pack sandwich bread. Jesus delivers a scathing rebuke: "Do you still not see or understand? Are your hearts hardened?"
In Mark 9:28–29, after failing to heal a boy, the disciples wait until they "entered the house" to ask privately, "Why couldn't we drive it out?" Jesus corrects them: "This kind can come out only through prayer." This makes no sense either - if prayer works it works by quality not quantity. Surely the disciples managed some quality prayer! If they were that disconnected from God what use were they?
In Mark 8:31–33, Jesus states plainly that he must suffer and die. Peter completely misses the point, takes Jesus aside, and rebukes him. Jesus fires back publicly: "Get behind me, Satan!"
In Mark 9:31–32, Jesus repeats that he will be betrayed and killed. Mark notes: "But they did not understand the saying, and were afraid to ask him."
In Mark 10:32–40, Jesus details his upcoming torture and crucifixion. Immediately after he finishes speaking, James and John approach him to ask if they can have the highest seats of political power in his kingdom.
Matthew and Luke changed these exact stories to make the disciples look
significantly more intelligent.