You may find that you respond to life's events, both mundane occurrences and unusual or even traumatic experiences, with similar emotions. That's because you're essentially riding the same wave, emotionally, and this has probably been apparent from the beginning of your relationship. You laugh at the same jokes and cry at the same movies, to start with; but as your connection has progressed and deepened, you find that you have similar responses to most things that life serves up.
This makes you feel bonded on a deep level, as if you possess twin souls, and you treat each other with great sensitivity and respect as a result. You feel supported by one another, validated because the way that you experience life is the same as how your partner experiences it, and vice versa. You share similar tastes in a variety of ways and, especially in the beginning of the relationship, you probably had fun comparing notes and discovering all the myriad ways in which you matched up! This won't and hasn't been the case in every single instance, of course; you could feel unpleasantly surprised on the rare occasion that you disagree on something, or have opposite emotional responses to an event. But as long as you can recognize that that's actually the norm -- two individuals experiencing life from rather different viewpoints -- and that you two share a special bond that not many couples have, you'll be able to appreciate this gift for what it is, and for what it offers you.