What I would add is you should feel a little bit of stress from the difficulty of the task. As an example, recently, I did research and in an unknown field both for the first time. I was a little tense, it forced me to focus every minute. If I didn't know what a formula or term meant in a paper I had to figure it out, because I had to be able to evaluate and possibly implement it.
I had to look at papers and evaluate them on their quality b/c I was using those to mold my own. I made many,many mistakes and failed hard many times. It was often very unpleasant (like running when you're fit but still not quite getting enough air on the last leg). But I kept pushing through. At the end, I learned more on this project than I had in a very long time.
Anyways, hope my experience can help someone else to push through and see the light on their project.