Being intelligent without grit is a curse. Imagine being so smart that everything you learn comes easy and all you have to do is listen, view or read one time, then it's stuck in your mind. New knowledge and skills applied overnight. You are surfing through life and most things comes easy. Until it doesn't.
The expression you lose what you don't use also apply to our exposure for handling difficult situations. The more we train our ability to endure difficult situations the better and more effective we become when next problem arise.
If you are trained to handle hardship then you have the confidence to approach any problem that will be thrown at you. This is the capacity and ability we want to reach for. Because our earthly intelligence is limited to earthly knowledge and that seems to change over time, usually very rapidly. Meaning, you need constant updates or you need to be really fast and nimble.
If you want to be cognitively free with the ability to problem solve and move on without being limited to a curriculum you need to accept hardship. Embracing the suck of failure. Your endurance will be a function based on your ability to withstand the learning reps.
Of course the most convenient way is to solve that problem with ease, to ace that test, to maximize that performance review without any extra effort. But the real world doesn't work like that. We cannot design the world to our abilities. We grow our abilities based on the world around us.