There are many good short quotes that can be used in a variety of situations. Here are some examples:
The best way to find out if you can trust somebody is to trust them. - Ernest Hemingway
We must accept finite disappointment, but never lose infinite hope. - Martin Luther King Jr.
If you want something done, ask a busy person to do it. - Unknown
Don't judge each day by the harvest you reap but by the seeds that you plant. - Robert Louis Stevenson