I know Heinlein advocated being a generalist.
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
I agree with him - to a point. I think specialization can give one a depth of knowledge that allows for breakthroughs and improvements. I think we should ponder deeply on a single topic from time to time, explore every angle of it, become an expert in it, then move on. I think after we move on, we should circle back to the in depth topics and look at them with refreshed eyes and a wider base of knowledge.
The thing is, you can be a specialist and a generalist. There is nothing in Heinlein's list that can't benefit from focusing on it and becoming more than acquainted with it, from becoming proficient and even attaining expert level. There are a couple of things on the list that most people live their whole loves never doing: conn a ship, butcher a hog, pitch manure, plan an invasion, fight efficiently. And we only get one chance at dying gallantly, so I'd rather not do that for quite some time, thank you.
Why should we specialize?
1. Having a skill set or knowledge in one area that exceeds that of most people means you will be the go-to person for that.
2. That translates into possibly something you can leverage into extra income should you need it.
3. Some fields of knowledge have gotten so large that being able to do every aspect of it well is actually seen as a liability because Johnson over there does can do Section A better than you ever will, and Brody can do Sections B and C better than you ever will - you will both be seen as and feel mediocre. By knowing the generals about the entire field and knowing what the field encompasses and yet also focusing on one part of it, you rise above mediocrity in that area. It's a very good ego boost to know you excel in that area.
4 Specializing can help you better utilize your time - you're not wandering back and forth collecting the tools because you didn't realize you needed this one or that - as a specialist, you already know the tools you need and have them ready. You use your time more efficiently so you can spend more time on leisure pursuits and maybe delving into a new specialty.
5. Specializing also allows you to understand better what and when you should add a new, related specialty to what you are doing. Specializing allows you to build up a solid repertoire in multiple areas over time.
I'm old, so I can see the patterns that lead me to where I am now, with an acknowledged expertise in several areas.
I started out as a generalist - as all children must. Schooling is a way for children to discover what they want to start out specializing in. Schooling that doesn't help them find that initial specialty is failing them.
I started out as a generalist, became a serial specialist and have, through time, become a generalist again, but this time, I retain all my prior specialties.
If I had jumped in to learn everything all at once I don't think I would have learned as many different things as I have and become the generalist I am now. It's all well and good for Heinlein to offer his list of what he thinks a human should be able to do - but he doesn't tell you that it takes time to learn and do all of that and more.
You don't start out designing and sewing haute couture - you start learning to thread a needle and the generalities of sewing, then you start specializing.
You don't start out cooking 5 course meals - you start by boiling water and learning the generalities of cooking. And then you start specializing.
David McCullough, Jr. at Wellesley High School told the graduating class they aren't special - and he's right. There they are, 400 people that have just accomplished the exact same thing, the exact same thing that hundreds, thousands of other teens have just accomplished all across the nation. There's nothing special in that any more. They have the potential to be special, to become extraordinary. Schooling is about giving you a taste of the different things you can specialize in by segregating the different subjects and allowing the students to spend a little time specializing in the basics and beginnings of each subject.
With any decent skill in the classrooms, the students will know where they want to start their specializations entering adulthood.
Pick a subject or topic you enjoy, learn as much about it as you can on your own, practice it, get certified in it (certification is over-rated and you don't need it, but honestly, the best way to learn something is to learn it from someone who is already an expert in the subject and if the only way to get that is through certification - go for it!), keep adding to your knowledge even after that. If you can sell your knowledge (teach it, sell the products of it, start a business with it, survive off of your knowledge of it), you're an expert but there will always be more to learn.
You can stumble into specialization, the way I did, or you can map out a flexible plan that takes you down a path you want to go. Either way, some degree of specialization is important to survival.