It's always too early to quit.
Either you run the day or the day runs you.
You never know what motivates you.
If you've got a talent, protect it.
If you can dream it, you can do it.
Know or listen to those who know.
Be gentle to all and stern with yourself.
I can, therefore I am.
To know oneself, one should assert oneself.
Be kind whenever possible. It is always possible.
One of the things that ultimately led me to leave mathematics and go into political science was thinking I could prevent nuclear war.