The humble oil tank seems such an innocuous component amid the extraordinary complexity of V6 Formula 1 engines and their hybrid parts. With all the millions of dollars invested in trying to make a success of a works grand prix operation, combined with the expertise of two mighty racing organisations, you wouldn't expect something so basic to be the root cause of calamity.
But that's exactly what happened in 2017. The unfeted oil tank is the chief reason why the McLaren-Honda alliance is no more, dissolved in a poisonous concoction of broken promises and shattered dreams.
Having made encouraging progress in 2016, invested time in helping the FIA to draft this year's new and enhanced aero regulations, and restructured the team in readiness to make the most of them, McLaren felt ready to catch up lost ground to F1's big three teams - Mercedes, Ferrari and Red Bull.