Compared to the other synoptic gospels, Mark describes the disciples failures in more depth. It is mentioned that they failed to cast a demon out of a child, despite being given the authority to do so. This does not necessarily mean that Mark is claiming this to be a failure. Perhaps he is emphasising the fact that only Jesus has the authority to cast demons out of people because he is the Son of God. If the disciples could cast demons out of people like Jesus, then what makes Jesus any different from them? For Mark readers, as well as for those who heard Jesus in the synagogue, Jesus is one with an authority far greater that of the scribes let alone the disciples. Jesus hits back at their failure claiming "you faithless generation." He is not just calling the disciples faithless, but the crowd too. So perhaps it is the crowd, as much as the disciple, who are to blame.
The disciples failure to stay awake at Jesus' hour of need in the garden of Gethsemane also features in Marks gospel. Three times Jesus came back to them and found them asleep during his hour of need. Mark shows Jesus being angry at his disciples for giving into temptation, however this could just show how Jesus doesn't give into temptation. That the Son of God has more faith than anyone in order to prevent himself from falling into temptation. Furthermore, Mark may be emphasising Jesus' ability to foresee things. If they failed to keep watch even for one hour they will fail the coming test, and that means that Jesus' words said previously, "You will all fall away, for it is written", will be fulfilled: they will fall away and deny Jesus by deserting him. On the other hand, it is interesting to see that Jesus finds asleep three times, which follows the three-fold pattern. Three times they fail to watch and fall asleep. We are not surprised, since Jesus warned them three times what was to happen to him, and they failed to understand.
Perhaps instead of Mark's Gospel being all about the failure of the disciples, maybe it is about his unique gift of being able to predict the future. It is shown on numerous occasions within Mark's gospel at the time of the disciples failures. Jesus predicts that the disciples would flee when he needed them as well as predicting at the last supper that one of the disciples would betray him, "Truly I tell you, one of you will betray me - one who is eating with me." If Jesus could predict the disciples failures then why did he not do anything to prevent them from actually happening? The fact is, Jesus needed the disciples to fail him like Judas, in order for him to fulfil his mission given to him by God. If Judas had never betrayed him then the last supper wouldn't have any significant meaning, nor would Jesus had been arrested that night and ultimately he wouldn't have been crucified. Moreover, Jesus also shows that even with the disciples failing him when he needed them most, he was able to forgive him.
Mark has many themes within his gospel, it is not just about the failure of the disciples. For example, he maintains a theme of urgency throughout his gospel by mentioning the word 'immediately' forty two times, eleven of which are mentioned in the first chapter alone. Additionally Mark also shows emphasis on deeds over words by spending less time on Jesus' teaching and more time on his actions than any other gospel.
Admittedly, the failure of the disciples is heavily feature in Mark's Gospel but that is only if you choose to believe that is what Mark is trying to say. For me, there are different interpretations to each of the disciples failures that I believe Mark was trying to get across. Throughout all the synoptic gospels, and even the whole of the Bible, there are stories that don't necessarily just have to be taken literally and I believe Mark's theme of the failure of the disciples is more of a metaphorical than literal.