What is an English words which describes that something is different for different people, or in other words, it's kind of exclusive to the person they belong to.
For example I want to say that there is nothing like "the-best-sleeping-duration". Sleep requirements vary with people. Different people have different sleep requirements.
Likewise, I want to say that there is nothing like the best method to study. Different methods are best-suited for different people. It's kind of subjective.