It is much easier when there is an air of possibility, when the future looks bright when you can see a way out. When the subject is something you are passionate about, when you are interested in learning more and excited about putting things into action.
But what about when the outlook is not that rosy? When you have to do things you are not interested in but have to learn anyway? Anyone that has tried to do anything of note - get promoted, start a company, get signed to a record label - has had to keep going through the tough times. They have had to be positive in the face of adversity. They have had to believe in a better future even when the present continues to look so bleak.
It is surely this ability to remain positive and focused no matter what fate throws at you that is the thing that separates success from failure, victory from defeat.
Being able to be positive though, is completely mental and nothing to do with external factors at all. Having a science background, I have been blind to this for a large part of my life. What was, in hindsight, cynical and destructive, I labelled as realistic. Of course, this is a self-fulfilling prophecy. If I think something will not work, then am I really likely to try past the first hurdle? It will just confirm what I thought, and I will give up.
Is there any downside to being positive in every situation? You will likely be happier, you will give more energy to yourself and those around you, and even if that particular situation does not work out, who cares? At least you give it your best shot with the best mindset. What is the alternative? To give up and be miserable? Go expand your possibilities.