What do you consider your most and least helpful advice you have ever given to someone? To who and why?

Most helpful: I told my friend to dump her lazy and inconsiderate boyfriend. Best advice ever because he became a junky.

Least helpful: I told my sister that her boyfriend is the one for her. Well, he had his fun with my sister and dumped her for another girl.

What do you consider your most and least helpful advice you have ever given to someone? To who and why?
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