Argentina is what happens when a task is too big for a coach and he loses the plot. By all accounts, Sampaoli is a good coach, but in hindsight, this was too much for him. He had settled for a plan and line-up before the tournament, involving 4 defenders, 2 midfielders, 3 attackers, 1 striker. By all means, it was only a draw against Iceland, but they had enough chances to score and did not lose the plot or shape.
Against Croatia he throws it all away and comes up with a line-up that his players are not comfortable with and where he hasn't picked even the right players for, because it's his preferred line-up. In the end, after the first goal scored, he throws even that plan to the sink and plays whatever that was supposed to be.
Not every great player turns into a great coach, but sometimes you just need coaches who have been through something similar to right the ship.