Because life's unfair.
Nobody has the perfect life.
We all have strengths and weaknesses. The most popular girls can be the most insecure and at the most risk. The nicest guys can be at risk of continuously getting rejected by people unwilling to be nice in return. The smartest kid can be socially awkward and consequently, secretly sad or depressed, as social acceptance is amazingly important to us teenagers. Stuttering further complicates the matter.