According to Dictionary.com, fortitude means:
mental and emotional strength in facing difficulty, adversity, danger, or temptation courageously
Fortitude is something that writers need. Writing can be hard and very often it forces us to face our inner truths and demons.
Weirdly, an image search for fortitude mainly returned pictures of trainers so I made my own. First, there’s the demotivational poster, just a reminder that taking things too seriously can be counter-productive.
And then there’s the seious one.
The artist who created the second picture (which is amazing) is Gild-a-Lily on DeviantArt, but I can’t find a link.
Boudica Marginalia 
Managers call it fortitude when you do what they ask, but stubbornness when you go against the grain.I preferred my picture of fortitude. A tank pointing its gun at a manager I worked for.