It's way more than just trigger discipline. There's the traditional rules of course:
Never point your gun at something you do not intend to kill
Be sure of your target and what's beyond
Trigger discipline
But there's also reasonable shit beyond the 5 basic rules:
Don't willingly put yourself in a situation where use of a gun may be warranted.
Property isn't worth killing over, especially in situations where you had to go out of your way to put yourself in perceived danger to protect it.
Don't block in the person you are trying to convince to leave.
People with guns commit more acts of violence than those who don't. Owning a gun is an irresponsible choice. There are more and there are less responsible gun owners, but owning a gun puts you and those around at a greater risk of violence. When all you have is a hammer ...
Generally they don't. There are a few certain models, like the Sig P320, that have some kind of deficiency where it can go off if bumped in just the right way. It's very, very rare, but it still happens much more often than others (due to it being a design defect and not a manufacturing defect, I believe).