"Is design subjective?", asks @cwodtke.
In everyday language, "subjective" suggests something based on personal feelings or opinions, while "objective" suggests something based on hard facts.
Since these are adjectives, I can apply them to different kinds of things. For example, I can differentiate between subjective and objective rules (priors) and subjective or objective decisions (futures).
In Design, you can take feelings or opinions, edify them as rules (along with objective rules) and then make decisions based on these rules. As long as the rules are shared or co-created within a subgroup, they are no longer just someone's opinion. This is why I think of design as being subjectively objective. Objective decisions (futures) made from subjective rules (priors). Things break when someone that does not adhere to those rules (or is not aware of the rules) interacts with those designed objects.
In Science, you take existing hard facts and do controlled experiments to generate new hard facts. This is objectively objective. The priors are universal (until proven false).
In Art, your rules are your own and so are your decisions. It is subjectively subjective.
In Medicine a doctor takes facts (say symptoms reported by a patient) and comes up with their opinion based on those symptoms. This is objectively subjective.
I think non-designers expect design to be objectively objective (like science), but when they realize it isn't, they assume it is subjectively subjective (like art). But it is neither.
(More nuanced Quora answer on the difference between subjective and objective)