This paragraph might come in handy. Why not attempt to raise motivation by inducing mental contrasting? "From where you are standing, work hard and you will get where you want to be" is a bit long, but seems like a good idea to me.
"From where you are standing, work hard and you will get where you want to be"
For a rationalist? It's an empirical claim that might be false. That's bad luck.
Is there any rationalist equivalent of "good luck"? I've tried a few variants, such as "work well", "knock them dead", "we're with you" and certain situation-specific phrasings, but haven't found anything that worked generally - though a hearty "may all the gods of Olympus be with you!" can serve. Not a vitally important point, but it would be nice to have something similarly supportive and yet accurate to say.