In traditional Japanese tattoos the Koi fish symbolizes perseverance. I believe there are many Japanese myths that have the Koi being rewarded for perseverance. In nature, there is the ant or the salmon.

There is also the little engine that could smile

Tattoos are very personal, so you should choose something that has meaning to you. I'm sure if you google words like perseverance, persistence and determination or the phrase "never give up" you will find something that resonates with you.

Good Luck!
Amy