It's a funny thing, guilt. I suppose we all feel it at some point in our lives. Surely each of us has done something that we later regretted. Sometimes it isn't something we've done, though. Sometimes it's something we haven't done.
It's interesting how different people handle guilt differently. Some people do whatever they can to try and make things right. Others sit back on the sidelines and ridicule that which has made them feel guilty. I suppose on some level these people think that belittling that which has created the guilty feelings in them will decrease its importance, therefore eradicating the guilt. These people are never successful at fooling themselves. The guilt creeps into their lives as excuses and paranoia.
The thing about excuses, though, is that there is always going to be somebody who has a better one than you who still came through. Somebody who is more sick or more broke or more whatever will still manage to get things done because they knew it was the right thing to do and they pushed through their excuses to make it happen.
Excuses cover over guilt, causing it to grow and fester like an infection. Eventually what seeps forth, like puss, is paranoia. People with hidden guilt see accusations wherever they look, whether they are there or not, much like Lady MacBeth's hands. I'm sure there's no need to remind you to what end Lady MacBeth came (hint: the guilt won).
The moral of the story is this: it is much more productive and healthy to deal with guilt in a positive way. Not only will you feel better, but you will maintain a sense of dignity and integrity that negativity prohibits.