It is easier to clearly reevaluate past actions or decisions than when they are being made or done; things are clearer or more obvious when they are reflected upon. A reference to the visual acuity of normal eyesight (20/20 vision). I can see now that having my brother as my legal counsel was unwise, but I guess hindsight is always 20/20. A: "I can't believe I was ever interested in such a self-absorbed jerk." B: "Don't blame yourself. Hindsight is 20/20, after all."