I don't know why you kicked a pole. There's no need to have extremely strong insteps because the only things you need to kick with the instep are the ribs, knee, and maybe the head. If you want to strengthen them, kick a heavy bag repeatedly.
A pole? That'll probably be best for strengthening up your shins, but not your insteps. You could easily break something since the instep is much weaker. But with proper control and accuracy you could toughen your bones up over time.
Yes, it's normal. Look up bone conditioning. Many styles of martial arts exercise what's called Wolff's Law. Look it up. Really neat stuff. It's amazing what the human body is capable of.
as i have told you before never strike anything harder then your bones
i kicked a pole really lightly and it hurt. is this normal at first? do JKD and teakwondo people strengthen the instep?