How do you make something second nature? Many things are so "second nature" that you forget that you even have done them. Do you remember every detail about getting up this morning, putting on your clothes, eating breakfast, or brushing your teeth? I don't think so. You were probably on autopilot and went through the motions. But, imagine of you suddenly appeared on earth and had never done those things. What if you had never eaten a breakfast before? Someone would need to explain, "now, this is a spoon. You bring it up to your mouth like this." etc. So, playing a musical instrument needs to become second nature, just like eating breakfast. That's why you need to practice everyday. Do you want to stop eating for a day? I sure don't. If I did, I would start to crave just about every kind of food. That's how it should be with practicing. If you miss just one day, you should begin to crave practicing.