I'm confused as to why you think that adding 'the' will make the sentences more emphatic. Where did you learn this?
Your first sentence is OK (although 'build up inspiration is a little unnatural). 'Curiosity' is an abstract and uncountable noun, so it does not take an article.
Your second sentence is odd - and as a standalone statement, it's wrong. It begs the question 'What curiosity?'. If you use a definite article, it means that we are referring to a particular curiosity, which is a strange concept. The only way that 'the curiosity' could be correct is if you were to define it, for example:
It is the curiosity which their teachers instilled in them that enables them to build up adequate inspiration.
Admittedly, this makes for a clumsy sentence, but the added relative clause ' which their teachers instilled in them' is necessary because it defines 'the curiosity'. It makes the distinction between this particular 'curiosity' (perhaps about science) and other types of curiosity.
Perhaps you should check in your grammar book again about the function of the definite article. When you use 'the', the reader or listener has to know which 'thing' you are talking about - but with a concept such as curiosity, this doesn't really work. The definite article makes the noun SPECIFIC, not emphatic. Emphasis is a different idea entirely.