Pessimistic about the path: "I'll succeed, but it won't be easy. I may find myself in some very difficult situations. I might not always know at first what I should do next. I might slip at times and might get scared. I'll have to tap into my reserves of endurance, patience, and courage before I finally reach the top."
In his book The Undefeated Mind, Alex Lickerman describes his ideas for strengthening your ability to handle adversity. One of his recommendations is to "expect obstacles". He describes research showing that people who expect tasks to be difficult tend to persist when things to wrong while those who expect tasks to be easy give up easily. He recommends what I see as a delicate balance between optimism and pessimism. In some of his chapters he talks about making vows about your important goals. In these chapters, I see him advocating optimism--confidence that for most of these vows you will prevail somehow, even if the outcome isn't exactly what you expected. And in the "expect obstacles", I see him advocating pessimism at least about what he calls "task difficulty".
I think this is a brilliant and all to rare balance of being positive and being negative. Most authors these days seem to push for nothing but positive thinking. The worst cases, to me, are the ones who tell you to just visualize things the way you want them to be and then wait for the mysterious power of the universe to manifest your dreams. Lickerman, instead, tells you to dream but then plan on a very tough road to reach that dream. Better to be pleasantly surprised when you reach that dream easily than to get discouraged and give up the first time anything goes wrong.