Motives for Goodness

In the book Kant brings up the question of whether or not people do good things because they know that they're good and because they adhere to a strict moral code or if it's because doing good things makes people feel good. This is an interesting point, but I feel like the problem with it is that it can never be answered for most cases and doesn't always apply. Someone who sacrifices everything and puts themselves into a terrible life for the good of others doesn't necessarily do it for satisfaction or even because they know it's right. An example of this would be someone who knows that an innocent person will be convicted of a crime and sent a hellhole prison so they volunteer to go instead so that the innocent person can be free and live their life. You would think that at some point in the prison the person inside would be completely miserable and regret it, but say they don't regret it. Suppose they say that the fact that the innocent person was able to be free keeps them from regretting it, despite the fact they they're miserable in prison, since they know that they would never be able to enjoy their life if they let an innocent person rot in jail. It would seem like this person is only doing this because they believe it's right and not for any personal satisfaction of doing a good deed, but it then could be argued that he's not doing it necessarily for satisfaction, but instead to prevent himself from feeling terrible about it for the rest of his life.
                        This brings up the question of even if you're not gaining any personal satisfaction from doing the moral thing, are you doing it because it's moral or because it'll cause you inner pain to know that you did the wrong thing. This seems like an important distinction between gaining pleasure from something and simply not letting it cause you pain. So if this argument is true it would make it even more difficult, if not impossible, to see what people motives actually are when doing the right thing.