I want to say that something is extremely challenging for both intrinsic and extrinsic reasons - for example, doing research on something happening on Neptune (intrinsic - Neptune is harder to observe) that is also politically charged (extrinsic - the politics get in the way of objectivity but are external to the thing itself).
I can say that, of course - I just did. But what if I wanted to use 'innate' (for its innate in-bornness) rather than 'intrinsic'? What is its antiword, if it exists? Perhaps some Latin way to say 'not inborn'?
Edit: I'm really specifically into reasons here, not skills or behaviours. An acquired vs. innate skill and a learned vs. innate behaviour are all well and good, but I don't think they are as good a fit for reasons.