Well, here's my take on it. You should do the right thing, even if your emotions say otherwise.
Say, for example, you had a sick pet, and the vet said he wasn't going to get any better, was in pain and needed to be put to sleep. Your emotions might say no, you want to take the pet back home with you because you love it.
But the right thing would be to let the vet put the animal to sleep so it wouldn't suffer.
So, he's saying if you let your feelings or emotions run your life, you'll make a lot of bad decisions. You should use your sense of what's right instead.
Of course, that's just my interpretation. Others may have a better one.