One of the important aspects contributing to realization of the 'zero' accident goal is what we consider 'accident' as or how we define/ count upon them. Based on the definition given in the current version of OHSAS, "any work related event that can cause injury, ill health or fatality is termed as an accident". Further it doesn't make much differentiation between an 'accident' and a 'near miss' and collectively view all such events as 'incidents'.
While it can be accepted that a 'zero' Loss Time Accident/Injury Frequency rate is achievable, it is hard to believe that a 'zero near miss' (a kind of 'accident') is ever achievable or has ever been achieved.
A 'Near Miss' speaks well of an accident which did actually happen and since everyone was lucky enough for not being there, no injuries sustained else the event took place due to lack of necessary controls. Infact one can experience several instances of such 'near miss events' in one's daily work life. If such instances are ignored while evaluating the status of accidents during a given period, one can reach close to the goal or even claim to have achieved it. A 'zero' status can't be claimed simply because no one was hurt while 'likelihood' still prevails giving rise to fateful occurrences.
And IMO, why a 'zero' status can't be sustained (if achieved) for longer is because we somehow can't eliminate all the contributory factors that crop up in the form of 'near miss' events which eventually translate into the kind of accidents where real injuries do sustain.