Mark moves fast!
John the baptizer prepares the people for Jesus, Jesus comes, is baptized, tempted, and begins His ministry after John is arrested. He calls four fisherman to be His disciples. Simon Peter is first, and also the likely source behind Mark's words.
Sins this reveals
Not confessing our sins when we are called to do so. Vs 5
Poor fathers do not take or express their pleasure in their sons and daughters. Vs 11
Giving in to temptation; not leaving other things to follow Jesus. Vs 18, 20