Learn French: Le courage dont tu as besoin pour surfer est difficile à trouver. - The courage you need to surf is hard to find.

We use à here because the subject of the sentence (Le courage) is the actual thing being found. When a specific noun is the subject and receives the action of the infinitive, we use an adjective + à + infinitive. If we used a general impersonal "it" as the subject, we would use de: Il est difficile de trouver le courage (It is hard to find the courage).

Why do we use the pronoun dont instead of que for "that you need"?

The French expression for "to need" is avoir besoin de. Because it requires the preposition de, we must use the relative pronoun dont (which replaces de + a noun) rather than que or qui. Literally, the sentence is structured as "The courage of which you have need."

Why do we use pour before surfer?

In French, when you want to express purpose—meaning "in order to [do something]"—you use pour followed by the infinitive form of the verb. Here, pour surfer translates to "in order to surf" or simply "to surf".

Could I add le at the end to say "hard to find it"?