Seattle is one of the most gentle cities I've ever visited and certainly the most gentle place I've ever lived. The weather is laughably mild, the safety of the downtown core (or really most neighborhoods with a Seattle zip code) makes the truly "rough" parts of other towns seem frightening in their foreignness, and the people are so deferential it's sometimes silly. Being from practically anywhere else in the country and indeed most other places in the world can make Seattle seem alternately passive and unapproachable. This deep-seated gentleness is often mistaken, especially by born and bred locals, as endemic aloofness, a subculture of standoffish behavior collectively known as The Seattle Chill. Personally, I don't buy it. Meeting people and making friends in Seattle is no more difficult than in any other city, and just like every particular region the process has its own quirks due to local flavor.
I grew up in the Midwest and I was surprised to come to Seattle where native Northwesterners are under the assumption that the vast swathes of farm land, suburbs and the occasional urban center folks on the coasts like to call The Flyovers are home to especially friendly people. I don't know where they get their information, but I never found my fellow corn-fed Americans to be any more or less welcoming than people from any other region. The truth is that no geographic locus has a monopoly on friendliness. The difference is in the idiosyncrasies of a given region that influence the way people interact. Midwesterners, to follow the example, may have their reputation for kindness because life in the Midwest is a bit slower and generally less exciting than it is elsewhere. Midwesterners are people of privacy rather than passion, so they affect the distance of politeness to protect that privacy.
There's a similar story in the notorious courtliness of the South. Southern hospitality is all well and good, plus it's refreshing to hear the formal language of every "sir", "ma'am" and "thank ya kindly", but that doesn't really mean that Southerners are inherently easier to befriend than Seattleites. That politeness merely serves as a first line of defense against potential conflict.
And therein lies the source of the so-called Chill. Seattle, being exceedingly gentle, is a town that really hates confrontation. I've had out-of-town guests comment on how easy it is to get thrown out of a bar here and how hard it is to start a fight. A friend of mine came out to Seattle and never quite got over the maddeningly deferential approach to right-of-way on the city's roads. Our problem in this city is that there's really no tonal bulwark in place for the inevitability of human conflict. Just like our infrastructure is woefully under-prepared for true winter weather thanks to the mildness of the average Seattle winter, our people are so used to the atmosphere of ease that they just don't have a way of addressing misunderstandings built into socialization and language. While the cultures of other regions have methods of handling aggressive behavior sewn into the fabric of local custom, Seattle is a place more or less devoid of any mutually accepted defenses.
The situation isn't hopeless, though. While it's definitely harder (that's harder, not impossible) to just strike up a conversation with a stranger in a cafe, it's actually pretty easy to meet people in Seattle once you understand the primacy of niche. You see, this town isn't just full of bars, clubs, cafes and concert venues, it's full of multiple variations on all those things designed with specific subcultures in mind. You don't just get a cup of coffee in Seattle, you get a coffee drink at a geek cafe from a menu with a Firefly theme and card games on the tables. Having mutual interests with those around you helps no matter where you are, but in Seattle it's practically mandatory. Know your interests, find where they're expressed in the landscape and settle into the comfort of being surrounded by people who will be more than happy to meet you on some sort of middle ground.