[lhnz]

Time might be scarce and you cannot specialise in both. However the separations between different subjects do not exist because of differences in the brain. We categorise subjects in order to aid in efficient dissemination of information. There are social reasons for the soft boundaries which formed in the past, but these are now reinforced by education and the workplace.

Likewise, skills are generally not mutually exclusive: the more mental models you have, the smarter you think. For example, there are some areas of UX which are relevant to API design. In fact, there are similarities between almost everything in life.