Cultural fit is very important. A lot of my hiring often comes down to it - I won't bring someone in who's a bad cultural fit even if they're brilliant because odds are they're going to be unhappy and leave, even if they're not the type of poor cultural fit that would negatively impact the rest of the team. I'm a sample of one here, but I have to hire good cultural fits because I have to try and retain in the long term, if not on my team, in the organization, because we're not in a top tier market for technical talent and it's hard enough getting good people over.

Anyhow, I'm telling you that to lead into this question - do you know what about the cultural fit isn't going well? All of us are bad cultural fits for some organization or another, but if you're getting that consistently, start looking bigger picture about yourself, and also the types of organizations you're looking to work with. There's going to be a pattern somewhere.

If this is happening with multiple interviews and organizations of various size and type, your best bet is to try and identify the factor and see if there's something you can change about yourself to whatever degree that's acceptable to you and/or possible. If you're primarily applying to the same kinds of organizations (let's say small tech startups in the bay area, just to give an example), maybe you'd be happier or more successful looking at a different industry/size/location.