Bee's. They know what they want. They know how to get it. They do it. Simple
To answer the question within your post, my interests have changed so much over the years, that I often feel like I'm having a mid-life crisis due to the fact that even I don't know who I am or where I'm going in life.
In just the last 12 months, I have gone from being fascinated with android programming, website building, psychology, hardware programming, and martial arts. I know very little about any of those topics, as just as I was getting somewhere with my self studies, I found something else more interesting and moved on. It's normal, for us, but frustrating at times.
My only advice is, if your interests become physical, take the safety precausions needed. And be careful with your money. Try to rationalize spending. Some of my books I've bought are anything but cheap
Enjoy yourself 