I think that having a positive attitude can help with recovery, but it isn't the main means to the end. There are so many advocates that positivity is the answer to all of life's problems and just by changing our attitude, we change the course of our outlook and our lives. The problem with this simplified method is that with PTSD, a positive outlook is something that has to be learned and cultivated. To think that it is a silver bullet, can leave a person feeling like a failure heaped upon the guilt pile of other over-simplified pseudo psycho methods.
Honestly, using the old tried and true methods such as CBT to change thinking patterns is a way to see things in a more realistic and at times a positive light. Life isn't all rainbows and unicorns, and the first time I realized that positives and negatives could exist in my cognition at the same time was almost a shock. Found out that I came out of remission last week and that is a huge negative, but the positive was there are at least seven new drugs that have been developed since the last time I had treatment. The realistic side said its going to be tough, but doable as there are options. Positivity has a place as long as it is grounded in reality and is not the ultimate end game.
Being "Polly Anna" is just a different form of the problem of denial or magical thinking.