The question isn't as simple as it may seem. On the one hand, we have to remember that our partners are not psychic - unless we ask, they have no way of knowing what we want. I've struggled with this situation for the better part of our 34 years of marriage.
What I'm going to type below, are shortcomings I've identified in my own experience - and may or may not apply to others. In my case, we married very young and never really learned to how openly communicate on matters of sex. Since our sex life was "ok", we prodded along and developed our lives, building a strong bond based on commitment and family. To the point where sexual disappointments weren't going to be justification for breaking up - but rather a burden we would endure as part of our commitment to each other and our family. But over the years, sexual frustration can tear you down and make you second guess your life choices.
Often times, I tended to think I knew what my wife's reaction would be before ever bringing up sexual variations - which lead me to manipulate the question or take a less than straight forward approach to making the request. If a partner senses this it can adversely affect their acceptance of the request. I would try too hard to avoid the possible rejection of an idea and end up feeling rejected before we had even approached the topic. Then if I did encounter resistance, I already had a head start on feeling sorry for myself. Another obstacle I created (in my mind) was transferring my lust for a particular idea onto my wife - imagining that she would get immense pleasure from whatever kinky idea I was going to suggest - only to be let down when she agreed but participated in a less than enthusiastic fashion.
My biggest problems were (and still can be) getting out of my own head and making more effort to understand what's going on in her head (as opposed to what I "want" to be going on in her head).
My biggest breakthrough was when I began to develop the mindset of - Here are things I like, and I'm ok if you don't feel the same way. But I'm not going base my happiness on your approval or disapproval. I won't press you to enjoy the things I do. But I will continue to urge you to enjoy them with me, but I'm not going to create resentment if you choose not to. Accept it or not, it's who I am.
Once I started thinking and acting in this way, I think it opened her eyes to the fact I had needs that weren't being met - as opposed to simply trying to control our sexual activities together. It also opened my eyes up to the fact that I really wasn't looking for what things she desired or needed - and working to draw that information out of her in open, honest conversation.
All in all, it has been a very positive step in the right direction but there is still much work to do after 34 years of being stuck in old ways. So, yes, it can still be disappointing when we fantasize and glamorize some sexual practice only to meet resistance - or even if there is no resistance, the act may fall short of our expectations. But we have to take some of the responsibility on ourselves and how we approached it, presented it, and executed it.
I'm still sorting all of this out for myself, so I apologize if my post kind of rambles on.