Acute stress is good (adrenaline -> fight or flight), chronic stress is bad.

So, worrying about money or being fired or <insert real life problem> all day every day will wear you down and limit your ability to reason. There's not much brainpower left over. This is why it's, for example, difficult to be super productive at work when you're going through a divorce or dealing with a breakup. And why it's never a good idea to launch a new product while moving house.

But, going bungee jumping or downhill mountain biking or racing cars or just driving too fast on the freeway. That's relaxing. Gives you focus, gets you away from the chronic stressors and into the immediate. Wonderful.