The 'unwritten rule' for non-tank pulls in dungeons

[Canadane]

I'm primarily talking about much earlier leveling dungeons,

"Tanks should pull everything" is a custom for level cap content, not levelling content.
Tanks that are pulling too much in levelling content are just asking to die. THere's an amount that's safe and an experienced tank may know this, but heck even I limit myself when not at level cap. Things hit you much harder.