The quote means that there's always a reason behind the things that happen in life. When people say this quote, they're usually trying to re-frame a bad situation so that a lesson can be learnt or a net positive can be highlighted. This quote can't be used for any situation. If you say this to a child who's been diagnosed with lung cancer and has 6 months to live, it's very inappropriate because there's not really a silver lining to dying young. May I ask why you think this quote has anything to do with stuttering in the first place.