Interest in others could very roughly be divided into two parts. We could say that there could be supportive or opposing interest.
For example, one could take interest into a poor guy for the sake of maybe assisting him to no longer be poor, or to negatively criticize him for being poor. Or maybe examine somebody’s words to spot something that is out of logical sequence and point it out to him, or to do the same in order to prove him wrong, bad etc. Those two are not the same. The difference is in intention.
People that -despite appearances- are busy acting against themselves most of the time, do the same to others most of the time. And one could go very wrong in taking another’s negative criticism into account in order to be good to himself and to others.