The trouble with self publishing is that the inexperienced person thinks producing the book is the issue. It's not. Producing a book is easy, it just takes time and money. It takes less time and costs far less than when I first started. Distribution is also less of an issue now there's print on demand and ebooks.
The big huge mega problem is SELLING the wretched thing. That means letting people know it's out there, and then persuading them to buy it. Then, when you've sold a copy, you've got to have a paper trail of some sort - receipts, invoices, orders, accounts. Publishers have whole departments devoted to these aspects: you have just you.
You will find it easier if you are writing non-fiction. If your book is about, for example, woodworking, the chances are you know there's a gap in the market for your book, that's why you wrote it. You will know all about which magazines, newspapers, TV or radio programmes are devoted to woodworking, you will know about woodworking societies, clubs, tool manufacturers. In other words, you know exactly who is going to buy your book, and how you can tell them it's out there.
Fiction is not so easy. It's a huge market potentially, but that makes it harder to reach. The newspapers and magazines which can reach this market are nigh-on impossible to get coverage - even traditional publishers struggle. Bookshops don't like self published works - you might get into your local bookshop assuming a) you have one and b) you're a regular customer and don't buy all your books from Amazon or the supermarket. Don't be deceived into believing all your friends and family will buy a copy. Some will, but surprising numbers won't, and you'd have to have an awful lot of friends to make it viable.
But my biggest reservation about self publishing is why I left it. I wanted to be a writer, not run a business. It was fun at first - ooh, the thrill of putting in fistfuls of cheques - but I didn't want to set up systems for processing payments and chasing unpaid invoices: I am not an administrator and have never wished to be one.
Self publishing is basically the same as setting up a widget-selling business, one where you also make the widgets. If you're thinking about going into self publishing you need to ask yourself: Do you really want to be a widget salesperson? Or do you want to be a writer?