Learn French: Quel soulagement, tu aurais pu tout paralyser ! - What a relief, you could have paralyzed everything !

While faillir means you almost did something, tu aurais pu is the past conditional of pouvoir and means you could have done it. They are closely related in meaning when talking about narrowly avoided disasters! To use this lesson's specific structure, you would say tu as failli tout paralyser (you almost paralyzed everything).

Why is there no article like un after Quel for "What a relief"?

In French, the exclamatory adjective quel attaches directly to the noun. Unlike in English where we say "What a", you never put an article between quel and the noun it modifies. Therefore, it is simply Quel soulagement.

Why is tout placed before the verb instead of at the end of the sentence?

When tout acts as the direct object of an infinitive verb, it must be placed directly before that infinitive. So instead of saying paralyser tout, the correct grammatical order is tout paralyser.

How exactly is aurais pu formed here?