I would point out that a psych/CS person could be really useful to a startup. Having more than just coding skills can be huge, and if anything you know about psych is related to behaviour, then you're golden. I'd like to point to this article about instagram by Nir Eyal: "But at its core, Instagram is the latest example of an enterprising team, conversant in psychology as much as technology, that unleashed an addictive product on users who made it part of their daily routines."
Yeah, I can get that. It was a lot harder but I finally got her moving foot in front of her pivot foot instead. Mental exercise for the day. I wonder if there would be external value in training your brain on adjusting these ambiguous images (the Necker Cube being a non-animated one).
Either/both. Someone who can just code is limited to that range of experience. Someone who can code and knows psych can not just code, but also use their knowledge of psych to shape product design decisions (e.g. Instagram) or even design software to solve problems in the field of psychology (either psychological problems people have or problems psychologists have). You get way more options by having not just one niche.