Punishing and rewarding (Help request)

How do I ask my 21-month-old son why he behaves the way he does?
When he does something he's not supposed to, I warn him. If he does it again, I put him on the hallway for 1.5 minutes. Then I explain why I did that and give him a cuddle. Now, when he does something he shouldn't and I tell him he'll go to the hallway if he does it again, he often stops already.....
Sorry, but I think kids become annoying if you don't give them consequences. I haven't become any less because of it. So I use the Jo Frost method and I believe in it wholeheartedly.

Also... I reward my son when he behaves in the supermarket, for example. If he doesn't behave, I ignore his behavior and don't reward him. Again, I explain it to him every time. I don't put him on the hallway in the supermarket, so that's how I handle it.
I also cuddle him to pieces.. because I love him so much! Good for attachment and self-esteem.
A child sometimes needs a firm hand... that will vary per child....