Construed in any literal sense, it is false. Until the development of powerful painkilling drugs and modern surgical anaesthesiology, for example, frightful extremes of physical suffering were simply a part of the human condition. The unendurable just had to be lived through. Happily, in the present era access to potent narcotics and the like means, for the most part, that we no longer need to rationalise such physical tortures with the desperate sophistries typical of the past. Yet the supposedly ennobling properties of agonies of the spirit are still widely respected.
Variety is indispensable to personal wellbeing.
As an empty verbalism, 'perpetual bliss' does sound fairly tedious. In a different age religious iconographers were able to derive much greater satisfaction in depicting the tortures of the damned in Hell than in evoking the curiously anaemic delights of Heaven. Potentially, however, there is no less a diversity of ways of being happy as of being wretched. It is a grim but accurate reflection of the human predicament that any notion of perpetual happiness evokes images of monotony. Yet whatever humanity's contemporary failures of imagination, within a few generations the experience of boredom will be neurophysiologically impossible.