In deciding to join a startup, are you more interested in the company's mission and goals? or are you more interested in the technologies you'll be using and the technical problems you'll be solving?
I care vastly more about the problem I'm supposed to solve than how I'm supposed to go about implementing the solution.
If I had the chance, for example, to work on a strong AI but I had to work in COBOL, I'd probably take that chance. Conversely, if I got to work with the coolest DWIM framework ever, but had to implement admin screens or other CRUD, I'd go absolutely nuts. It's the difference between dealing with accidental and essential complexity. If there's not enough of the latter on the horizon, I get very antsy.