On the road to competitive gaming, it's easy to get jumbled in a chorus of often conflicting advice and data. What I want to open up with a scalpel is what happens when people repeat ideas given by others over and over until there is no real conversation on a given unit or tactic's use.
Even good ideas, when they're practically dogmatic can become bad ideas in certain circumstances. There are blogs on the internet such as this one dedicated to gaming, but there are also forums and websites where things are discussed ad nauseum. Posters who get sort of persona dramatis status usually do so because they have a record of success or are viewed as the elite amongst a flood of amateurs.
These personas need only drop a condescending helpful hint that x unit, y wargear, or z tactic is the correct one, implying contradicting posters are obviously wrong, to scare off new posters from using contradicting methods. However, worse is when new posters don't read the historical discourse and ask the question.. garnering responses from peripheral posters espousing the original thought that they are immediately wrong. Then it becomes the telephone game. People start repeating advice without knowing the context of why and how it was given. It's not ALWAYS a bad idea to take hunter-killer missiles on all your tanks if your intent is to form an alpha strike style list. 100 points to have 10 more S8 shots on T1 may be totally acceptable to you.
Eldar are definitely an army that new people are basically given a list of good and bad based on community affirmed knowledge and not any thought on the tactics, models actually owned, or anything else the original poster had behind his/her list.
Not to say these opinions don't change. I believe that they do. For a while, it was considered forum etiquette for at least one person to suggest a new Eldar player load up on a Seer Council (wargear up for debate somewhat) and that they were the icepick to the enemy's skull. However, in recent months I've noticed a switch. People previously touting mechanized or jetbike councils have been somewhat mute. When people post that they are making a list with a council, there are usually voices to suggest they neuter the squad for point vs. efficacy reasons--or drop them altogether in favor of the newest spam units like Dire Avengers and suicide Fire Dragons.
Use these communities to see what other people view as 'the norm,' competitively, but do not take it as the gospel. For a while people thought the only viable build for Eldar was mechanized until players like Blackmoor started winning - not just friendly games mind you - but tournament games regularly with a ground pounding list using some pretty unorthodox units. I found it easier to just rip these forums for knowledge about how people play the armies that I don't get to face often. I read army codices for ideas on how I would play them and make army lists to fit that theme.
If I read the Imperial Guard codex and I am suddenly filled with awe at the idea of a mass troop blob assault guard list -- you know, something ridiculous like 150 guardsmen backed up by Straken, a couple of eviscerator missionaries, several armed commissars, and a good bit of artillery backup -- then I want to know how to make my vision work, not be told something like 'Drop the missionaries, they suck' when they are, besides Straken, the heart of the strategy. It may be a simple strategy. It may be weak in the end, but when people don't give you rationale besides knowledge they gained as mere hearsay, they aren't giving you sound advice. I'd probably get told to take 6 Vendettas, 5 Vet squads, and a Company Command Squad and call it good right?
My point exactly. People want advice, or at least tried and true reflections of why their intended strategy could/will fail. They don't want you to tell them they are incapable of playing unless they use the newest flavor of the month list. Take care to form strategies in your lists to counter the newest lists, but don't drink the kool-aid before you test the waters yourself. Proxy that Vyper before you write them off because someone told you they suck or they don't fit in your list. They may be repeating conventional knowledge that turns out to be not so conventional.
Sometimes, my friends, moar dakka isn't so great.