If a result is not used much, then its veracity does not matter much for the rest of mathematics. 

Otherwise, there may be several proofs of the result, which makes it much more probable (in a general sense) that the result is true. Importantly, there is usually some explanation or understanding of **why** the result is true, that is, the ideas behind the result. 

Also, people try and do construct counterexamples to disprove a result, if they do not see why the result should be true.