In The Rise of Superman, Stephen Kotler talks about finding the sweet spot of flow. Not too easy, not too hard. Just right.The state of flow he’s talking about is that “in the zone” state people talk about when they’re extremely engaged in what they’re doing. Creatives talk about it with writing, painting or drawing. Athletes talk about it when they’re surfing, skiing or mountain biking. Hours can fly by in what feels like minutes. It can happen anywhere and any time but there are a few requirements that have to be in place to make it happen.One of the requirements is the difficulty of what you are doing has to be just right. What does he mean by just right?I’ve heard this one called the goldilocks principle of being just right. It refers to the difficulty of the task being hard enough so it's not boring but not so hard that it’s frustrating. It’s in the zone down the middle.Of course it changes over time as you get better at what you do. As you engage in something at a level that increases your skill (not so easy it’s boring) then you’ll get better at it. That will raise the level of difficulty that you need to really engage your interest.If you are a skier that loves black diamond runs, then black diamond or a bit above that is going to be engaging for you. It’s going to require a lot of focus to not crash but it’s still a lot of fun. Where as if you were going down a green run, that’s probably way to easy for you and you’ll get bored.It can be hard to gauge where exactly you want to be so your engaged without getting frustrated. Stephen says to go no more than 4% higher than your current skill level. Any higher than that and you’re going to hurt yourself or get frustrated.I’ve been there myself. Surfing with friends that are far better than I am, they look for waves and conditions that are interesting to them. What’s great for them is going to be too much for me. I’ll get throttled in waves they have fun in. Instead of being 4% higher than my current skill level, they might be 20 or 30%. That’s going to hurt.Stephen tells his own story about mountain biking with a bunch of pro friends. They were amazing downhill riders, flying through the trails, getting huge air and nailing everything. Stephen spent a year trying to learn and keep up but just couldn’t do it. He was just injured all the time.Taking a step back, he realized he was too far above his 4%. He started riding by himself and with friends that were at a similar level. He gained more experience that way and was riding with his pro friends within a year. He had to reduce the skill level jumps to less than 4% and then his learning really picked up.Instead of being frustrated (and injured) when he was trying to ride too high for his skill level, he toned it down and rode within his 4%. He found more flow and learned faster at the same time.