A common idea was &quot;any single system fault shouldn&#x27;t make catastrophe by itself&quot;. Nowadays it&#x27;s &quot;any single fault shouldn&#x27;t jeopardize the mission and any two faults should still allow for safe return of the crew&quot;. The redundancies are designed in accordance to this.<p>From this perspective Gagarin would die if both accelerating stage worked longer and retrorockets failed. Only one of this two systems malfunctioned - so, barely, he managed to return unscathed.