If I start reading something on the internet, I have to either read it through in one go, or take a break midway through and finish it after checking email or whatever else. If I don’t want to do either, then that suggests I don’t want to read it, or I should save it and not even start it now.
The amusing thing, of course, is that I’m currently breaking this rule to write this. But that’s the reason it should be a rule.