Why doesn't the button to check if the combobox is full work?

Question

C++ / C#

private void button1_Click(object sender, EventArgs e)
        {
            if (comboBox2.SelectedIndex < 0 )
            {
                button1.Enabled = false;
            }
            else 
            {
                button1.Enabled = true;
            }

Answer 1

SelectedIndex cannot be less than 0

Answer 2

Give a man a fish - he will be full for one day, give a fishing rod - ... although it may break)
We put a breakpoint on the check and press the button.