Here is the situation:

We both have 7 cards in hand. Plots revelaed: Rule be Decree and Blockade (my plot). I have Golden Tooth Mines on the table. Do Rule be Decree working?

"When revealed" effects resolve before any other passive effects. Since both of you have the same number of cards in hand, Rule by Decree would do nothing and then you would draw a card for having revealed a plot card.

So i didnt mistake. I didnt allow myoponnet to do this.

Thanks:)