If Hidden Blade loses its target (e.g., the target flashes), why don't you get the draw effect?

Ruling: When Hidden Blade resolves and cannot find its target on the battlefield, it cannot kill the unit and therefore cannot determine who the controller was, so the draw effect does not trigger.

Sequence:

• Hidden Blade resolves
• It looks for its target on the battlefield
• Target cannot be found (due to flash/removal)
• Cannot kill the target
• Cannot determine the controller
• Draw effect does not occur