My stop loss on this stock is 0 (0 is a stop loss, it does not mean you do not have one! Many people say they do not trade with stops. Well that simply means your stop is not determined and you do not have your strategy fully understood.)
Risk: I am willing to lose 10% of my capital if this company goes bankrupt (stock goes to 0).
I am willing to experience a drawdown of 5% on my capital if the stock gets cut in half. While possible, it is relatively unlikely from the $260 level. I see $155 as the worst case scenario (a flash crash could take Tesla to this level, or some horrible quarter after quarter). I have buy limits sitting at $160 in case a flash crash occurs. Those of you that traded on May 6th 2010 would understand where I am coming from. Those that haven't, I suggest you back-test that trading day. You could also take a look at major losing days like August 24th or 25th (can't remember) 2015. Getting stock really cheap has a lot to do with being many steps ahead of the game.