Always desire to learn something useful.

The line urges a habit of continual learning, but with an emphasis on practicality: knowledge should be directed toward what can be applied in life rather than pursued as mere ornament. Read in a classical Greek ethical frame, it aligns with the ideal of cultivating wisdom (sophia/phronesis) through experience and instruction, and of shaping one’s character by seeking lessons that improve judgment and conduct. In modern quotation culture it often functions as a concise maxim about lifelong education and self-improvement, though its attribution to Sophocles is frequently secondary (via later anthologies) rather than securely tied to a specific surviving play or fragment.