☒ There isn't really a rule, but more practices that I've come about. Basically, and whenever possible, instance variables shouldn't go in a partial. It's too easy to reuse the partial and forget to declare the instance variable. Generally, if there is a nested situation like [@ticket, comment], this would be a situation where if the @ticket wasn't assigned then there would likely be a lot more problems. However, it is still "good" practices to avoid the instance variables in the partials if possible. On top levels, i.e., a new action sets an instance variable and this renders new.html.erb, I would be a lot more likely to consume the instance variable within that new.html.erb.