The Lorentz transformations were initially applied by Lorentz to two observers, x, y, z, t and x', y', z', t', one being at rest in the ether and the other in motion with the velocity u.  Lorentz had regarded t as the true time and t' as an artificial time.  If the observers could be persuaded to measure time in this artificial way, setting clocks wrong to begin with and then making them gain or lose permanently, the effect of his supposed artificiality would just counterbalance the effects of his motion through the ether.

For Einstein they were observers moving with any velocities whatever subject to their relative velocity being u, and that t and t' had precisely equal rights to be regarded as true time.  In Einstein's view, these equations were even more general in that they were not concerned with the possibility of an observer being at rest in ether, or indeed the existence of an ether at all.  The general interpretation is this:  If one observer O, having any motion whatever, finds, as a matter of observation, that light for him travels uniformly in all directions with a constant velocity c, then a second observer P, moving relative to O with a constant velocity u along the x-axis of a coordinate system belonging to O, will find, as a matter of observation, that the light, for him also, travels uniformly in all directions with the same constant velocity c, provided he uses, for his observations, co-ordinates (sic) which are connected with the co-ordinates of O by the equations of transformation.

In this example, the equations of transformation are:

    x' = B(x-ut)
    y' = y
    z' = z
    t' = B(t-ux/c²), where B = (1-u²/c²)^-1/2, of the expression:

        x² + y² + z² - (ct)² = 0, representing the outward moving spherical wave front of light emanated at the origin of x, y, z at t₀.

Essentially what we have is the transformation of a rigid Cartesian coordinate system of three orthogonal spatial axes and a time axis into another identical coordinate system in motion and displaced from the first, the observers themselves being unessential.

It is also reasonable to think that one can repeatedly perform these transformations from one coordinate system to the next, which if faithfully executed would cause no variation of the original variables.  In order to do so, the Lorentz transformations must be altered to fit the transformation back, such that as, x' = B'(x'-u't'), where B' = (1-u'²/c²)^-1/2 and t' = B(t-ux/c²);  yielding x = (1-(-u)²/c²)^-1/2[(1-(-u)²/c²)^-1/2(x-ut)-(-u)(1-u²/c²)^-1/2(t-ux/c²)] = x,  which is correct.  Notice that u' and -u and that both time (t or t') and the speed of light (c) drop out entirely.

What this means is that as one commits to these transformations to one system to the next, only the basic Lorentz geometry's prevail rather than observational variables such as motion and time, suggesting in turn that relativity pertains to phenomenal behavior only.

Taking Einstein's analogy concerning his special or restrictive theory of relativity, such as an observer on a moving train, without windows to see out, one can relate inertial behavior, such as the vertical tossing of an object by the train's observer, to conditions relative to the train track by Lorentz transformation with regard to the mechanism of such behavior.  In other words, though in tossing the ball vertically upward we can imagine instead a curved path relative to the tracks, its mechanism remains unessential to our understanding of what we observe, much in the same way that inertia and gravitation are interchangeable to observational evaluation within a closed inertial system.  Furthermore, such transformations need not concern themselves with either time or motion, since these are not fundamental, but rather phenomenal to the observer, and in the least, within the observer's domain, detectable variations.

Thus, though the executions of such transformations, the investigator has the free option to choose non relativistic tenets, such as the instantaneous simultaneity of events, providing such excursions are restricted to this secondary frame of reference different from the observer's own.  For example, the observer may choose time t₀ at the origin O within his own frame of reference occurs simultaneously to time t'₀ at the origin O' of the secondary frame of reference.

The investigator may also say that the secondary frame of reference is unbounded and that all other frames of reference are inclusive to it, being inside it, or that its rest motion at O' corresponds to the average vector motion of the speed of light, where the variation of individual quanta from this value, might be their observed velocity.  In this sense, the measured velocity of light c, would be the deviation of the observed quanta from null rest of the light.  Since there are no imposed restrictions to the evaluation of physical systems within this secondary frame of reference, the investigator is free to impose numerous challenges to its behavior, and or perhaps mechanisms, to the extent that all events which occur, occur simultaneously to t'₀ at its origin.  If the investigator chooses, and is able to support it, even the notion of ether wind is allowable, as it is also allowed by relativistic principle concerning phenomenal behavior.

The point is this, that relativity is applicable only as a statement of the phenomenal behavior or reality, and not necessarily fundamental, and as such, its tenets are not necessarily universal.

Metaphorically, or even pragmatically, if the observer cannot see out of the train in order to evaluate the external mechanism affecting behavior inside his coach, what can he gain by stubbornly refusing to engage his imagination to the outside world by using the same tools which have locked him inside?