Why does Decius say an idea is not possible?
Well ultimately at the end of the day every idea is possible, however some ideas/featues that are requested require massive changes to the core gameplay or additional overhead in terms of how the game retrieves/updates information in the system which make them extremely unattractive to add.
It is different when you are starting a new game as you can code in a ton of features at your leisure and make sure they all work in synchronous with each other and that no feature is going to hinder another, however once a game is fully established some changes can just not be made becuase of performance issues or because it will alienate half of your community.
So in general when Decius says an idea is not possible it is not that he thinks your idea sucks or that he hates you it is simply that the idea just is not possible to be implemented in the game the way things stand.
So please do not think just because Decius says no to your idea it is because he doesnt like you or is being a meanie it is simply that he doesnt wish to ruin the game by introducing locking errors, performance related issues and other nasty things when the game is running like a well oiled machine.