I Didn't Know My Own Strength by Whitney Houston. The lyric is inspiring and uplifting.
I didn't know my own strength. I crashed down and I tumbled.
But I did not crumble. I got through all the pain
I didn't know my own strength. Survived my darkest hour
My faith kept me alive. I picked myself back up
Hold my head up high. I was not built to break
One of my favorites for when things are difficult is Survivor by Destiny´s Child.
Destiny's Child Survivor Lyrics https://www.youtube.com/watch?v=Ki97oF8LBFE
This video has the lyrics. In case you are wondering, the lyrics on this video are not written in grammatically correct format, they are written the way the girls pronounce them, some of which are highly reduced leaving off large portions of a word or complete words. For example the ¨word¨ gon in the lyrics is not truly a word. Gon = ¨going to¨