The quote is essentially about the importance of character, and the need to create or adopt one if you don’t already possess a strong one. The first part, “One must keep one’s character,” emphasizes the importance of maintaining integrity, consistency, and moral strength. It’s about being true to oneself and sticking to your principles, even when faced with challenges or temptations.

The second part, “Earn a character first if you can, and if you can’t, then assume one,” is a bit more complex. It suggests that if you don’t naturally have a strong character, you should strive to develop one. This could involve cultivating virtues like honesty, courage, and perseverance, or working to overcome personal flaws. If this proves too difficult, Twain suggests that you should then “assume” a character. This could be interpreted as adopting the traits and behaviors of someone you admire, essentially using them as a role model.

Applying this idea in today’s world, or in the realm of personal development, could involve a few different approaches. One could be to engage in self-reflection and self-improvement, working to strengthen your character and live in alignment with your values. Another could be to seek out role models or mentors who embody the kind of character you aspire to, and learn from their example.

In the age of social media, where people often present curated, idealized versions of themselves, this quote is a reminder that character is not about outward appearances or public perception, but about who you are when no one is watching. It’s about being true to yourself, and striving to be the best person you can be, even if that means having to work at it or borrow from others’ examples.