So what I'm not understanding is if, "I bring a smile to the Queen's lips by playing a tune" would be challenged and possibly fail, why is it phrased that way at all. Why wouldn't the player just say, ""I try to bring a smile to the Queen's lips by playing a tune?" In both cases the intent is the same and there is going to be a challenge that could fail, but only in the latter does the phrase not contradict one of the possible outcomes.
Because I have never played in any roleplaying game, ever, where the GM has not had final say. Yes, I could play D&D and say "I try and swing my sword at the orc" or "I try and walk across the room", or "so long as it makes sense to the GM, I'll drink the ale in front of me" but it's just a waste of words. Everything my character does is subject to challenge from the GM or other players, always. So the "I try to" is just straight assumed. Everything can fail.
I have one player who very much likes to preflight things; they will say "my intention is to try and get the king to agree to fund us, because I think he secretly does want to go to war", but it slows the game down. Because it invites an out-of-character discussion every time you say "I try" it doesn't help with immersion either. I'd much rather have people just say what they do and correct them if it needs challenging.
Maybe this approach is influenced by how I direct plays. I much prefer an actor to try something (assuming it is not going to endanger or embarrass a fellow cast member) and me say "yeah that works" or "umm, like the idea, but not the way it looks" rather than stop the action, ask permission and then, virtually all the time, do it. My players are also pretty competent, so I'd prefer to trust and adjust, rather than stop to get permission.
YMMV; but for me as a GM there is very little difference between "I try to bring a smile to the Queen's lips" and "I bring a smile to the Queen's lips". They are both statements of intent, and both subject to adjustment and resolution.