I already explained that. But here goes:
One, the official rule is that both skills are used: Perception to find the door, Investigation to figure out how to open it.
Two, because neither I (who said Investigation) nor the other person (who said Perception) really care. We weren't quoting the official rule; we were showing what the section on skills said and how the skill descriptions indicated that the skills we chose could be used to find secret doors. Again, you failed to acknowledge the existence of an actual rule involving finding secret doors. You're quick to "gotcha" people but very slow at admitting when you're wrong.
And the answers we gave weren't contradictory, just different. It'd be like if the question were "how do you inflict damage" and one of us said "use your action to make an attack roll" and the other person said "use your action to do something that makes the other person have to save or take damage." Two different methods, both perfectly within the rules, not at all contradictory.
Yes, they are contradictory. Because they are different answers for doing the exact same thing. How do you inflict damage can be answered in a hundred different ways because there are a hundred different, rules defined, ways to inflict damage. Your answers actually conflict because if I sit at your table, I roll one skill, if I sit at the other table, I roll another skill, and there is no way for me to know which skill will be used beforehand. It seemed a pretty simple question actually. How do you find a secret door? Apparently, in the well defined ruleset of exploration, you either roll perception or investigation, and it's up to your DM to tell you which one it will be.
I don't fail to acknowledge the existence of the rules. My point is, the rules are actually contradictory. I can't know, as a player, before sitting down at your table and asking, what rule will be used. This is most certainly NOT true in Combat. How do I inflict damage in combat? Well, here are fifteen different ways you might do that, depending on what your character is. At no point does it say, "Ask your DM".
Aaand you still didn't answer my question. Actually, you didn't answer either of my questions. I feel that if our positions were reversed, you'd be quick to point that out, perhaps with a condescending "ROTFLOL you can't even answer a simple question!!1!" as is your wont. And so I shall ask them again. Perhaps this time you'll actually answer them.
1. If you have a party that includes a ranger, and you come across a flood, does the DM say "nope, no matter what you do, you can't cross"? Do you try to come up with other solutions and the DM refuses to allow them to work? If so, why do you think that's a problem with the rules and not with the DM? Have you spoken to the DM about this behavior? Have you considered getting a different DM, since this one seems antagonistic?
To be honest, it's a fast moving thread and I didn't see your questions. But, remember, the flood is YOUR side's reason why the ranger's powers are not working. That wasn't my example. The flood only came into being when the DM realized that the ranger was bypassing the challenge. And, yup, I speak to the DM about this behavior. And I'm told that nope, it's not "railroading". It's a "natural consequence" of the setting and how dare I question the DM this way.
2. Why do you claim that nobody has come up with exploration rules for D&D in 40 years? There are exploration rules in the 5e DMG and in several other books for this edition, there have been exploration rules in every other edition of D&D, there are probably hundreds of websites with information on exploration in D&D or interesting encounters (many of which are non-combat) or things to find while exploring, and lots of 3pp books, such as Level Up, being produced by this very site, and AiME, which I know you know about. Wouldn't it be more logical to say that you simply haven't researched them?
Because I don't claim this? Again, you aren't bothering to read what I write, so, why do you keep replying to me?
My point is that exploration in 5e is made trivially easy by the presence of a number of very common class elements. That there are people who write about exploration challenges doesn't surprise me. Lots of DM's think that sudden floods are a "challenge" too.
Like I said to Lanefan. This thread gets extended ad nauseum because every time any criticism is brought up, it's automatically passed off as bad DMing or appeals to authority. At no point can we actually get to the point of discussing possible solutions because I have to constantly waste my time trying to run at this wall of trying to convince people that the problem exists in the first place.
I mean, good grief, I POSTED my solution to the problem. Dice pools and mechanical frameworks based on character stats that leverage class and character abilities in order to overcome challenges. I immediately get told to sit down and shut up.

Instead of spending all this time trying to tell me why the issues I'm having don't exist, why not take a stab at trying to resolve the problems?