When in a RP game, the GM offers creative freedom, the ability to allow you as players to direct the story, and you have an idea, so you put it forth into motion. It's not something that will hurt the GMs story, it won't affect any other player, you simply put the idea out there in hopes that the others will back you up and add their own ideas.

And then someone tramples on it with their own idea and overshadows your own.

I get that we all wanna be the hero of our stories, but I find it really rude to use the "creative freedom" gift given to us to push your co-writer's ideas into the ground just so you could have your character(s) in the limelight. If you have your own idea for how the arc should go, I think stating so in the OOC or even via private message would be a better idea than posting in IC and letting it rest there.

This doesn't happen often, but I noticed it in a game I am playing on a different site and it just irked me.