you can see why in the fill method of the Model
public function fill(array $attributes)
{
$totallyGuarded = $this->totallyGuarded();
foreach ($this->fillableFromArray($attributes) as $key => $value)
{
$key = $this->removeTableFromKey($key);
// The developers may choose to place some attributes in the "fillable"
// array, which means only those attributes may be set through mass
// assignment to the model, and all others will just be ignored.
if ($this->isFillable($key))
{
$this->setAttribute($key, $value);
}
elseif ($totallyGuarded)
{
throw new MassAssignmentException($key); <--- only if totally guarded
}
}
return $this;
}