Let's talk about two different scenarios when you bring up your army list to other 40k players. Going to let you guess which is brought up more. I honestly wonder why.
JJ typing, First up Goldilocks Scenarios, as I call it.
This is the game where everything works perfectly and nothing goes awry.
This a rather simple scenario to describe. You make all of your To Hit, To Wound rolls and Saves. Your opponent deploys foolishly. A round at a tournament with someone who has never played before. Opponent has nothing that can stop your tanks or heavy hitting squads. This can go on and on, which is more of an exercise in redundancy or beating a dead horse.
Now for the other side of the coin. The side of the coin so many Haters, and others, love.
This scenario is also easy to describe, yet is described more often
Getting the basic ones out of the way: dice go bad, bad match ups shooty-Tau against close combat Orcs. Forgetting key models at home and having to put other models in the army because the game is WYSIWYG. Now onto those scenarios that we hear when bringing up our lists. You talk about your Wraithguard list and someone brings up poison weapons, you bring up your Necron Solar Pulse list and someone brings up Tau Black Sun Filter, you talk about your Canoptek Scarab farm and someone brings up IG pie plates, these examples go on.
You can prepare for one while putting yourself more at risk for other lists. List tailoring is advantageous. However you can't list tailor for pick up games or Rogue Trader Tournaments, one day tourneys, or Grand Tournaments, multi-day tourneys. While goldilocks scenarios are rare to come by, it seems doomsday scenarios are everywhere. On the table, internet and 40k shop talk over food and drinks.
The question at the beginning of this post stands. Why do 40k players always bring up doomsday scenarios when someone is talking about their list? I never do this because it is not in my nature to piss in someone's cheerios. Now be a general asshole and sort of unfriendly, that I'm intimately aware of. But to come up with ten reasons why someone's list won't work. Or poke holes in someone's idea. Purposely, notice I typed 'purposely', steal someone's thunder. Never understood that.