why is adding first electron favorable and adding 2nd electron unfavorable?

Question

Electron Affinity 

Answer 1

Since it appears you are studying electron affinity, based on your tag in the question, I would answer you this way. 

The first electron affinityis negative (exothermic), and the 2nd electron affinity is always endothermic (positive). This is because the 2nd electron is being added to an ion which is already negative therefore it must overcome the repulsion  

Answer 2

Can you specify the element?  Because, for example, oxygen would love to have two electrons...