[pocksuppet]

Never hold a net short position.

You may hold a short position as part of a net neutral or net long position with extreme caution.

[eru]

What you are saying suggests that there's a single number (that can be positive or negative) that characterises your net short or long position.

That's silly.

You can build pretty much any kind of shareprice-to-payoff function with enough options and other instruments. And that's one dimension (a line) more than just a single number. You can get arbitrarily more complicated, if you want to.