13 The question is whether disparity, or lack of disparity, in sentence is capable of giving rise to a justifiable sense of grievance: Lowe (610). Whether there is a justifiable sense of grievance has to be determined by taking into account the application and effect of relevant sentencing principles, including the totality principle: Nguyen v The State of Western Australia [2009] WASCA 8 [27]. That principle is discussed in detail in Roffey v The State of Western Australia [2007] WASCA 246 [24] - [26]. It is sufficient for present purposes to note first, that the practical effect of the totality principle is ordinarily to arrive at an aggregate sentence that is less than that which would be arrived at by simply adding up all the terms appropriate for the individual offences. Secondly, once the sentencing judge has determined the appropriate total sentence, the orders for cumulation and concurrence reflect the practical need to achieve the mathematical outcome. A variant to the above approach is to reduce the otherwise appropriate length of the individual sentences and order greater cumulation, as did the judge who sentenced the appellant here. Thirdly, a rationale for the totality principle is that there is assumed rehabilitation and reduced demand for retribution after the initial sentences have been served. As a consequence, there is not a linear relationship between the number of offences committed and the length of the total term.