As a corporate trainer, I frequently caution managers about using the word "FAIR", and actually use taxes as my example by asking "What would be a 'fair' tax system?"'; adding that you don't have to believe it to suggest it.
The answers are ALWAYS:
Same %
Same $
ZERO TAX (always comes up third or fourth)
"according to their needs" - always a response from a particular personality type, like everyone's "needs" can be met
Usage tax
Sales tax
Graduated tax system (theoretically, what we have)
Close the loopholes (to make it fair, theoretically)
Any one of these can be (reasonably) argued to be "FAIR"... and just as reasonably, be argued to be "UNFAIR". Then I tell the managers to NEVER use the word "fair" in their compensation/promotion/performance meetings with employees because FAIR is not an absolute.