I think it's important that we always make the effort in every part of our life. It could be anything; our education, our job, our relationship, our goals. If we always know that we tried, did our best and put effort into everything we do we can never feel guilty about the outcome.
It's not easy to put the effort in all the time, not unless you really want something and are motivated. We feel guilty when we know we could have done better. I feel that way about many things, but I know there's no one to blame but myself.
It also goes that if you're going to do something you should do it well. If you choose to help some one you shouldn't do it half-heartedly, you should show someone that your happy and willing to help. If your working for someone, doing a job, you should be the very best of whatever that role is that you can be. If your in a relationship and you love someone you should never stop showing them that. If you've got a goal to achieve something, it's up to you put the work in to getting to your goal.