Often technical personnel who are not familiar with security techniques think that restricting access to ports on a router or firewall can protect a network from attack. Why is this solution ?

What will be an ideal response?

When a firewall prevents any traffic from entering or exiting a network on any well-known port, such as port 80, you have indeed closed a vulnerable port to access from hackers. However, you have also closed the door to Internet access for your users, which probably isn't acceptable to your company. The tricky (and almost impossible) part for security personnel is attempting to keep out the bad guys while allowing the good guys to work and use the Internet.