Playing someone else's game

So I was watching a game of Warmachine tonight (damn you OT!) for about 15 minutes and I think I made a critical gaming error.  The error is:  Playing someone else's game.  Giving advice is one thing.. especially to a rusty player that hasn't played in a couple of months.. but giving him the game winning scenario is just wrong.  I don't know what I was thinking actually, it must be all this overtime that's frying my thinking process.

Here's what happened:  It was 35pts of Retribution w/ Kaelyssa vs. Cygnar led by pNemo.  Both of these guys are my friends so it was a fun, casual game.  At the end of the Retribution player's turn, Nemo had like 5 HP left because of Backlash and mass shooting had that left a Lancer dead, a disrupted Charger and a dying warcaster.  As a Cygnar player, I looked at what my friend had left over and the game winning strategy came to me immediately.  Keep in mind that the Cygnar player hasn't played in god knows how long.. so he's still fiddling around with his cards and re-remembering what his units did.  Like a dipshit, I blurped out:  "I think I see a caster kill here".  I didn't go out and say what order of operations he needed to do to secure absolute victory, but I watched as my words sank in and guided his Defender to take a boosted shot at Kaelyssa that left her with 7 hitboxes.  Needless to say, I went back to my desk and minutes later, my other friend (the Retribution player) texted me that Cygnar won after I left.

Now's the time to feel like ass.  As much as I wanted to help the Cygnar player, sometimes the best thing to do is just watch as a bystander.  Advice is one thing, but a game winning tactic should be kept mouth-shut until the game is over.  It's not as bad in 40K and WHFB because the game isn't as sudden death like WM is, but that's no excuse.  After the game, you can brag, laugh and slap eachother in the face all you want, but during the game, there should be a "no advice zone".

Just wanted to share with you this quick experience.  I'm sure it's happened to everyone and I know no one likes a passenger-seat player messing with your game.  This is one of my biggest pet peeves in all of wargaming and I really fluffed it up today.  Alright guys, your turn.  Story time GO!