The phrase "ignorance is bliss" suggests that not knowing certain things can lead to happiness. It implies that sometimes, being unaware of troubling facts or harsh realities can shield us from worry and stress. In other words, if we don’t know about something negative, we won't be affected by it.
The phrase "ignorance is bliss" originated in the 18th century and is often attributed to the English poet Thomas Gray, who wrote in "Ode on a Distant Prospect of Eton College" (1742): "Where ignorance is bliss, 'tis folly to be wise." It reflects the idea that sometimes wisdom and knowledge can bring about distress rather than happiness.