It's always too early to quit.
To know oneself, one should assert oneself.
If you think you can do it, you can.
Go for it now. The future is promised to no one.
Do not weep do not wax indignant. Understand.
Be gentle to all and stern with yourself.
Quality is not an act, it is a habit.
Be thine own palace, or the world's thy jail.
Things do not happen. Things are made to happen.
If you're going through hell, keep going.
In hard-core science fiction in which characters are responding to a change in environment, caused by nature or the universe or technology, what readers want to see is how people cope, and so the character are present to cope, or fail to cope.