The argument
Discovery Channel's TV show 'MythBusters' discovered that it would possible for both Jack and Rose to survive on the door if they tied a life jacket underneath to make it more buoyant.
Premises
Counter-arguments
Critics point out that the MythBusters result was obtained under calm, controlled conditions and required deliberately tying a life jacket beneath the panel to add buoyancy — a solution that is obvious with hindsight in a warm studio but was not available to two exhausted people in darkness and near-freezing water, where hypothermia and shock set in within minutes and fine motor tasks quickly become impossible. That a stunt team could make the door float two people does not show that Jack and Rose, in the moment, could have calculated and executed the same fix before the cold killed them. James Cameron has also observed that the buoyancy was ultimately set by the script rather than by an experiment — the scene was written for Jack to die — so a physics demonstration about what the prop could bear does not settle what the characters could realistically have done.
Rejecting the premises
[Rejecting P1] The MythBusters test measured whether the panel could physically bear two people in calm conditions, not whether two freezing, exhausted people could have discovered and executed the fix in time. [Rejecting P2] Adding a life jacket underneath requires calm, coordination and time the characters did not have; critics argue hypothermia would incapacitate them before such a manoeuvre could work. [Rejecting C] That a survivable option existed in principle does not mean it was available in practice, so the conclusion overreaches from a controlled experiment to the real scene.