The primary sources for depression are physiologic, our body makeup, and life challenges.  As to life challenges, sometimes we're upset over things that we cannot control and other times how we responded and our limitations.  

I made a significant mistake, unfortunately I am not well-organized.  I am happy about how I responded and perhaps this approach can help others, 

1. Candid but limited (im time) self-evaluation  Own that you made a mistake and write it down.  Its like your boss or coach dressing you down.  

2. Identify cause and solutions  Usually there is not one cause of a problem but several, so try to identify what could be done better.  Self-improvement is hard so you might go through this process several times, and your improvement may not be complete.  However, candid-self evaluation can make you better.  I used to lose things when I was little, baseball gloves, jackets, school books, and felt bad and sometimes did not want to tell my parents because of the cost.  Now, I try to develop a program- leaving a hotel I take a comprehensive check of everything in the room, I'm one of the last people off the plane after again checking.  Still can lose things in other circumstances, but it is getting better.

3. Compliment yourself   If you do go through 1 and 2 diligently, compliment yoursel for your success, against don't expect complete change.  If a student doing poorly in math raises his grade from F to C-, he is doing better.  Don't keep focusing on your failure and instead recognize that you have taken meaningful action to improve yourself and that is all that can be done. 

4. Work on accepting that which you cannot change  You may have other things in life that cannot be changed,  consider what can be done long or short-term and somethings need to be accepted.  Many people who work in household are depressed about their jobs, but I saw a woman in Aruba.  She said she worked for a hotel as a housekeeper and had a wonderful life- sometime things are a matter of perception.  

Good luck.  I am not happy I screwed up, I am happy that perhaps I can use this to make someone else's life better.