When good things become common in my life, I wonder if I truly still appreciate them as much as I did in the beginning. This makes me wonder if good things can only be appreciated in relation to their absence or their opposite. Is pain needed to appreciate pleasure? Is death required in order that we appreciate life?
Are there known philosophers or philosophies that have considered this problem of necessary oppositions?
If we assume pain and pleasure are opposite and exist on a continuum, there must be some sort of neutral point between them. Things can be neither pain nor pleasure. The average of the possible experiences is neutral.
If we only experience neutral things and pleasure, then in fact we have moved the baseline. The average is now halfway between what "was" neutral and the most pleasurable thing we've experienced. Pain is always defined as the low end of the scale.
If we connect this to real-world pain and pleasure, we get into biology. Pain represents harmful things for an organism whereas pleasure represents good things. If all you had was "good" and "really good", really good would be the new goal, the new pleasure. Organisms would evolve to feel discontent or pain when they are not gaining an average amount of "good".
In other words: When you have less pain, the baseline moves, make what was pleasurable before become less pleasurable or even painful. Similarly, lots of pleasure broadens the spectrum and also increases the baseline (beyond the again biological effects regarding novelty).
The short answer is Yes we do need. However, we need to be careful in defining those terms.
Pain and pleasure are relative terms and is completely subjective concepts unlike "absolute truth" or "number of objects" etc. What you consider pain might be a pleasure to other people or other people might assert that your "pain" is a pleasure to them but only by a slight degree.
This is not a black and white situation, there is wide spectrum and unless you cross a neutral point, "pain" might be a "lesser pleasure" the key point to note here is that we are comparing one situation to the other.
But coming back to you, when you say that you are feeling "pleasure" you have inherently already made the comparison to other average experiences of your life therefore, you have defined it as pleasure. Consider a thought experiment you have been gotten rid of all your memories and experiences. The first experience you will get after that will neither be pleasure nor pain since you don't have any other entity to compare it to.
A scientific analogy I could give is that you cannot measure a true potential of a physical body but only the potential difference between two bodies thereby requiring a comparison.
Are there known philosophers or philosophies that have considered this problem of necessary oppositions?