I think that forget-to-attack mistake is kinda trivial. Almost never happened to me or my opponent before, not counting dc. Next time, maybe you should introduce more important mistakes like fail trading, play minions instead of removals, wrong minion choice, etc.
I've seen Trump do it more than once.
I think the important & completely valid lesson that can be taken away from the OP's example, is to not rush your turns.
Everybody should follow a strict & methodical process each turn; something like:
Do you have lethal.
Formulate this turn's plays, keeping in mind:
Possible combos between board & hand that might determine order of play. (Sea Giant, Cult Master, etc etc)
Effects & abilities of your minions. (don't forget you've got a Wild Pyromancer on the board! or that your Venture Co. Mercenary should be the last minion you play! etc etc)
are you the aggro, or control? should you trade, or go face?
Given prior plays, how likely is my opponent to have the cards in-hand necessary to kill me? (Your turn's play should aim to keep this to a minimum)
is the game likely to go long & so require you to extract maximum value from your hero power?
If part of your turn's play involves card draw, and the draw can be done first, it should be.
Am I taking too long planning? some more complex plays can take quite a while to execute due to animation delays. In such cases it's ok to start the play without having the entire turn mapped out.
I've done my play; is there nothing more I can do?
I've seen Trump do it more than once.
I think the important & completely valid lesson that can be taken away from the OP's example, is to not rush your turns.
Everybody should follow a strict & methodical process each turn; something like:
Did you consider coining the chow?
You look to have a very aggressive opening, and it would have been useful for protecting your cleric.