If only older me could have advised younger me that a pink knit tie and white pants might not entirely impress my colleagues at my first internship.
That’s an extreme example, albeit a relatively harmless one, but most people would likely have benefited if their younger selves knew what experience has taught them. That’s especially true in the workplace, where sometimes you have to make a mistake to learn from it, but in many cases, you would be better off if someone had just helped you avoid the error.