Well I think the hard part is knowing when they will play it. They obviously have it in the deck but to maximize your play you need to know exactly when.
Is it brawl on turn #5, 6, 7, 8, 9 or 10? Etc.. For example if I mulligan and end up with a muster, and top deck another muster turn #4.
You play like they have Brawl in their hand from turn 5 going up.
So I muster turn #3 and Druid swipes. Do I play muster turn #4 (let say I didn't get a shredder)? Does he have a 2nd swipe. Yes or no? And if he does will he play it.
You play Muster again with Impunity. This example is easy. They spend Swipe to clear part of one card (you still have the weapon from the Muster) and then they do it again to clear one card again. You actually want them to use the 2nd Swipe because after that they can't clear your board. A good Druid player will probably not Swipe just a board of 3 tokens unless he strongly suspects a Quartermaster is incoming.
Another easy example is let say Druid hold 3 cards on turn #10. I can set up for a two turn lethal or I can clear his board (let say I'm sitting on 20 hp). Do I push for win and if he has combo then he has combo I lose. Or do I play around him having combo. Continue to clear the board and try to stay above 14? You can't exactly know you can only make the best educated guess on how he has played. There are scenarios where both are the right play.
You play around combo all the time every time. If you clear his board then you are playing it safe and increasing your chances to win. If you try to set up a 2 turn lethal and they had combo in hand... well then you are going to feel pretty bad about it afterwards.
You only don't play around combo if you are not going to win otherwise. Let's say you are running out of cards, already on very low health and he has heavy advantage. Basically you are going to lose if he has combo anyway so in that situation you DON'T play around combo because otherwise you will never win (just lose slowly or lose when they eventually top dick combo).
I think any idiot can play on curve but that isn't the hard part the hard part is when you get shitty draws and how you can play from it. Like when I watch Hoej play his secret paladin so many times he wouldn't make the trade and just go face. Now him being a top player he just seemed to almost always top deck what he needed for exact lethal, but obviously would look like an idiot if that Truesilver/blessing/consec never came for that extra 2-4 damage to push for win. Now obviously he sees something that tells him to push rather than control the board so it isn't luck. It's a educated guess with probably some math/odds behind it.
That just comes from experience. Usually as a Secret Paladin you can make an estimate on what's left on your deck (ie. look at Deck tracker) and say "ok he has used up his heals and if I go face I can set up a 2 turn lethal on board with extra damage from hand. Next turn I can kill him if I just top dick 2+ damage. I have 4 cards in my deck that can do 4 damage which is good chance to get. Even if I don't get it I would still be in OK spot."
As to someone like Trump who probably can't make that play because of his inability to know when to say fuck value/board and push. When can I push and say he doesn't have his AOE or he won't have it in time. When do I know he does have his AOE so what's the best way to play around it and when is my lethal turn coming? What can he top deck that would ruin my game, what can I top deck would ruin his plans?
There's no easy answer to these questions but there are general guidelines.
*You always assume they have one AOE clear in hand so you play around that. Once that is played, odds are they don't have a 2nd AOE right after that so you play a bit more aggressively after that but not too aggressively in the off chance they do.
*If you are winning then you have to be extra careful about what card they can use that can put them back in the game. If you are winning and you think you can set up a 2 turn lethal by playing 2 extra minions but playing those 2 minions means you would lose to Lightbomb... then don't play those 2 extra minions to set up a 2 turn lethal.
*If you are losing then you can't afford to play around board clears and have to start playing for tempo/closing the game fast.
Of course this all changes from match up to match up. Against a Freeze Mage you would have to play a bit more aggressively to pop Ice Block if it means playing into Frost Nova + Doomsayer sometimes. Against a Druid/Oil Rogue.. you would play extra safe even at 20 HP and clear their board completely, even if it's an inefficient clear (like using Consecrate to remove just one minion).
All these things come from experience. That balancing act of playing safely vs playing aggressively/playing to win and how to switch from one to another seamlessly.