You're also left with /just/ that. You can say your character is being alert, you can describe him as perceptive, but with no mechanic to back you up, you're back to DM judgement calls. Sure, it's out in the open - you know the system has given you no mechanism with which to model your character in that case, the 'game' is reduced to your ability to advocate for your character and make decisions for him, thus 'gaming the GM' or 'Gygaxian skilled play' - I like to call it 'player as resolution system.' The character you're playing doesn't matter anymore, just your ability to make a case to your GM.
That's all you really have with the design of most mainstream game designs anyway. Consider a traditional perception or knowledge check. Here are the judgement calls a GM in a mainstream game generally makes in order to resolve them:
- The Content of the Fiction
- If a Check is Called For.
- The Difficulty Class of the Check.
- Any Bonuses or Penalties That Apply.
- Whether to Reveal the Difficulty Class If It Is Even Real.
- What Success Means.
- What Failure Means.
The entire body of the rules remains firmly under the control of the GM. Even if a check is successful there is no guarantee that it will provide real information you can use rather than a chance for the GM to impart bits of world building or color. It implies a certain amount of real machinery that gives some players solace, but is ultimately illusory. Pay No Attention To The GM Behind The Curtain. It might make you feel better about what happens, but it is just as subject to GM judgement calls as a more fiction oriented approach. It also makes it more difficult to see what is going on from the player's perspective, especially when we have a culture that does not see GMs and other players as equals at the game table. We might be able to use the rules as a form of coded language to indirectly address the fiction, but I feel that is all we are really doing.
I feel like a directive like always say what honesty demands that is every bit as much part of the system in use has the potential to have far greater impact. It shifts the cultural fabric of the game to one where players are allowed to expect principled decision making from their GMs and see where they are acting against the shared interests of the game. Part of what I enjoy about running a game with explicitly stated principles is that those principles become a measure by which the other players can hold my feet to the fire. It allows us to course correct and helps to keep me honest. Also when we keep things closer to the fiction it becomes far easier to see what is actually going on and tell if my framing was off.
I am not saying there is no use for mechanisms. We know how to structure mechanisms that can have a stronger impact on the social dynamic at the table. The specific questions that read a charged situation obliges a GM to answer truthfully if you succeed does far more to encourage GMs to impart useful information. The way Blades in the Dark represents actions according to effect and position(risk level) encourages transparency, negotiation and powerful expectations of what results should look like in the fiction. Although I am not really that much of a fan of explicit stake setting and intent based resolution much of the time it does create powerful expectations that enable more informed decision making.
I would add that I believe we should be careful that whatever game we use does not short circuit skilled play of fictional position. I think Things On Character Sheets can serve to increase our interests in the fiction and relate it to us in a way that can more effectively be gamed, but the beating heart of any roleplaying game should reside in meaningful exploration of the fiction. I also have no significant issue with judgement calls. I just think we should be applying our judgements in principled ways that enable greater player investment in the game and impactful decision making.