Role-playing means a lot of different things to a lot of different people. We could probably make a big mutant Venn diagram. If we were so inclined. For the record, I'd say "role-playing means creating a fictional character and then performing them within the game's fiction/play environments". This definition says nothing w/r/t/ any previous play experiences or what affect they have on your current PC.
Put a little more thought into it and you would realize your last sentence is just plain absurd.
A fictional character within the fictional environment of the game would not inherently have any knowledge of what your previous characters did. Nor would they have previous detailed knowledge from the monster manual of all creatures likely to show up nor their number of hit points and special abilities. They would also not know everything found within the campaign setting guide, nor would they have precise knowledge of the future and details about NPCs you encounter as a result of you, as a player, having played or read the adventure previously. Not unless special allotments were made for each of these things.
Your own definition specifically includes regards to one's previous play experience by the two elements inherently being a "fictional character" and the "game's fiction" as both elements naturally create a set of bounds within which you are expected to choose your actions. Abusing player knowledge is far more egregious violation of the two principles you set forth than listing your characters a "Lawful Good" and then molesting, robbing and killing all NPCs you come across and have the ability to do so.
If you have a character act on knowledge of these things that the fictional character within the fictional environment would not have knowledge of, then you are not taking on the role of a fictional character within the rules of the fictional environment. Therefore, by the definition you yourself gave, you are in fact not roleplaying if you use player knowledge.
You are simply utilizing a set of stats against other blocks of stats in order to earn points. You may as well simply be playing an electronic game with the game guide revealing all the games secrets open at your side and all the game cheats activated.
No.
I mean, sure, that's how you like to roleplay, and if you're having fun you're doing it right. But it continues to amaze me how many people think that this one type of roleplaying...and honestly a kind of trivial, simplistic version of it...is The One True Path of roleplaying.
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I notice that in nothing you wrote, not one single solitary sentence of it, did you remotely come within the general region of actually debating the topic at hand. You went off on some weird tangent about people only talking as though they were in character.
The topic at hand it using player knowledge in character.
Reading the monster manual and using knowledge of its stat blocks to easily overcome the creatures.
Using knowledge from the campaign setting guide in order to gain an advantage or dismiss challenges.
Reading the adventure ahead of time and using that knowledge to avoid all traps, extort NPCs and prepare for all surprises and twists well before they are revealed.
That is the topic at hand. Not only speaking as the character, not limiting ones dialogue to "period proper" speech. The topic is abusing player knowledge in order to avoid character challenges.
If you want to debate against me that abusing player knowledge in order to maximize character advantage without limits is still somehow roleplaying, that is what I am talking about. I am not your imaginary strawman who is saying you need to reflect your character's mannerisms and dialogue at all times.
This is a very specific point. If your character does not have knowledge of an easy win mechanic, a coming plot twist, NPC motivation, trap location, etc... you should attempt to feign ignorance about it as much as possible.
Imagine if you were watching the first Star Wars and in the first scene when Luke meets the droids he said "oh!! Hey! You guys are running from my Dad, right? You got that message from my sister! Well, let's go give the message to Ben Kenobi. That's Obiwan. But first I need to tell my aunt and uncle to go to the city for a while so that they don't get killed by the Stormtroopers or Sandpeople or whatever later. And then we can to to the Cantina to meet with Han and Chewbacca, they are the ones who will fly us to the Death Star. But we need to make sure we don't split up inside or Obiwan will die. We'll meet up with Biggs on the rebel base later."
Yeah... that's such a worthwhile story you have there. It is SUCH a good thing that Luke's player read the adventure ahead of time to make sure he maximizes his success.