Fortitude is one of the four Cardinal Virtues, along with Justice, Temperance, and Prudence. Other words I've seen used for this are Courage and Strength. Many tarot decks use Strength, but I prefer Fortitude because I think it's easy for people to misconstrue the concept of strength with the physical instead of the mental and spiritual.
For my tarot deck, I used a woman getting a tattoo that says, “Nil desperandum” which is “never despair” in Latin. This is about inner strength, which is especially needed during times of emotional upheaval or turmoil. It’s about perseverance in the face of adversity. Think about the tattoo symbolism here. A tattoo is not like getting a bandage ripped off. Tattoos take time to do, so you have to suffer through them. But the pain doesn’t last, and if you make it through, there are great things waiting on the other side. With a tattoo, it’s easy to put your mind on the end result. With life, this is more difficult, but never despair.
“Don't pray for easy lives. Pray to be stronger men.” ― JFK
Think back on troubling times before and you’ll see what you’ve made it through. If you're going through the worst time of your life, think back in time. There was a previous moment that was the worst moment for you, right? You made it through that. And the time before that. And on and on. Life never gives us anything we can’t handle, and coming out on top through a harrowing experience enhances our character and makes it easier the next time. Don’t forget previous experiences. You’ve made it through everything else. You will again. There is nothing you cannot handle.