I have to fight against this tendency to believe past was better almost every day. My mind seems to try to trick me every time i'm making progress in life, bringing memories of a better past, showing why today sucks.
The solution? Reason. I just ask myself: Ok, that was the good part. Now, try to remember the bad ones. Oh you can't? So it's obviously a fake memory pal. There were no such time in my life without difficulties.