Year-round mild weather, world class dining scene with foods from just about every culture, incredible hiking in every direction, amazing urban parks, beautiful scenic vistas everywhere you look, world class cycling, incredible museums, world class surfing, easy access to skiing, 2 hours to wine country, high walkability and ability to live without a car, great biking infrastructure, large number of career opportunities, many educational opportunities, endless events and parties, a massive gay scene, interesting and open minded people with a 'live and let live attitude' that allows others be themselves, a general vibe that encourages people to explore who they are and find their passions - no one here is gonna ask you when you're going to 'settle down' or have kids. I could keep going but I doubt the person I'm replying to will even read this far.

It has its downsides like high cost of living, homeownership being out of reach for many, the intractable NIMBYism that tries to crystalize the city in amber, public transit that's often inefficient and frustrating, business cartels that block new restaurants and shops that might bring competition, and a more carrot than stick approach to dealing with the drug-addicted homeless population but anyone who says SF is an unlivable shit-hole either hasn't spent any time here or has very different ideals and just doesn't like cities.