Unloading a too heavy concrete box with an excavator by a bad operator

The action took place in Brazil. An excavator operator tried to unload a large box of concrete.

Some big mistakes.

1. The heavy weight of the concrete box was not taken into account.

2. No chains were used to lift it.

3. The excavator operator did not choose a stable position for the operation, losing the balance.

Which do you think was the biggest mistake?

A task like this could be very easy for an experienced excavator operator.