Learn Spanish (Latin America): Uno deja de esperar cuando la balsa se hunde.

The phrase dejar de followed by an infinitive is the standard Spanish way to say "to stop doing something." While parar generally means to physically stop moving or halt an object, dejar de is used when quitting an action or habit. Also, remember that in this context, esperar means "to hope" rather than "to wait."

Why does cuando trigger the indicative se hunde here instead of the subjunctive se hunda?

You use the indicative after cuando when stating a general fact, a habitual action, or a completed past event. Since this sentence expresses a universal truth or general observation, the indicative se hunde is correct. You would only use the subjunctive (se hunda) if referring to a specific future, uncompleted event, like "I will stop hoping when the raft sinks."

Why do we need the pronoun se in se hunde?

Without se, the verb hundir is transitive, meaning to sink something else (like an enemy sinking a ship). By using the pronominal form hundirse, the action becomes intransitive and stays with the subject. The raft isn't sinking another object; it is simply going down.

Is using uno the only way to make this a general, impersonal statement?