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)