An idiom is a commonly used expression whose meaning does not relate to the literal meaning of its words. An idiom is a group of words established by usage as having a meaning not deducible from those of the individual words (e.g. over the moon, see the light).
Slow and steady wins the race...... as the tortoise would say
The theme is to make the best decisions for you life as you can.
The tone is dark and depressing.
Hope this helps, love :)