Optimism can be hard for those of us that are naturally pessimistic or even "realistic".  I put quotes around realistic, because that is what pessimistic people tell themselves to feel like they are so negative.  It is actually ignoring what optimism is for people to call themselves realists.  Optimism is not about ignoring the bad things going on.  It isn't about not helping yourself when things go bad or just hoping that magically things will change.  Optimism is taking what life is, and trying to figure out what is good within that situation.  Optimists still look to better their situations.  They can find good things in bad situations and then look for even better things in other situations and how to get to them.  Optimists are more happy while making changes, they practice gratitude regularly.
Pessimists on the other hand, only see that they are on their back and can't get up or walk.  They lament that they will die soon and not notice the beautiful view they are given.  They may be too focused on the negatives to notice the refreshing breeze that if you moved just right, might help you flip back over.
If you are reading this going, but Lauren, I'm a realist.  What do you truly mean by that?  Optimists aren't ignoring the fact that they are stuck on their back.  They are ignoring the fact that if they don't flip over bad things will happen.  But they are enjoying the journey.  Think about the optimistic people in your life, or that you know of.  Their lives weren't amazing with no problems, but they recognized the beauty and learning opportunities during the difficult times.  
As a reformed pessimist, I know the difficulties in finding the positives within negative events.  I modeled the optimistic people in my life, and when I slip back into old patterns, I recognize my gratitude towards those optimistic people and work towards seeing the opportunity in a bad situation (even if that is just getting away from it and learning the dangers of that situation).

Your inner voice is not always your friend.  When you are depressed or anxiety your inner voice may be your worst enemy.  Cognitive Distortions get in the way of our rational mind and positive thinking.  One mistake does not make us a loser or terrible.  We make mistakes all the time.  Rarely is one mistake world ending.  Remind yourself that no one is perfect and if someone was perfect they would probably be obnoxious.