It's not "naive" but rather "unrealistic" to believe there is ONLY ONE person in the whole wide world of (almost 7 Billion) people who would "get you", love, adore, and appreciate you for who you are. My guess is there are thousands of people across the planet that would fit that bill if you were able to get around to meet them.
However the truth is most of us set up our own limitations/requirements. We naturally seek to "exclude" rather than "include".
We say she/he has to be of a certain race (that eliminates billions of people right there), they have to be of a particular faith (another group of billions are eliminated), they must be from my own country, (this also narrows down the field), they must already live in my town or at least same state.(Another large segment of the world is eliminated)
And then we start to list our "personal requirements" such as (age range), height, weight, education & income level, hair/eye color, never been married before or does not have children. We then look at their habits (smoking, bad credit/debts, drinking, drugs...etc), their friends and family, shared goals/dreams in common, chemistry, sexual compatibility, and Does the "timing" coincide with what we want to accomplish?.....etc Last but not least we are always "evoling" (Mr/Ms Right) at age 21 may not be our ideal type of mate at age 31 or 41.
Then there are times when you have "found the one" however they don't believe YOU are the one. Therefore by default that makes them NOT the one.
I don't think people "settle". I believe with age comes wisdom and we learn to be "practical". We also come to realize that we're not "perfect" either. You come to realize when it comes to relationships it's not so much about "right" or "wrong" but more about "agree" or "disagree". Finding someone who wants what you want and agrees with you on how to obtain those things is the basis for a long-term relationship or marriage. For the most part "like attracts like". Most of us don't look like movie stars and most of us are not going to end up marrying someone who looks like one either.
"Don't expect to sit next to the moon unless YOU are a STAR!" One man's opinion! :-)