Katsunami, cost is a big factor in this, particularly if you happen to write very long stories. When writing, for many of us, is something we do in a our spare time because we enjoy it, justifying the cost of competent professional editing can be difficult - especially when any realistic look at publishing has you understand that you may never recoup the expense. Of course, you then have to consider that lack of professional editing may end up being the reason why you fail to sell books. The old rock and a hard-place conundrum.
I agree with most of what you've said Lemurion, and there are tricks to aid self-editing. For example, I've found that read-back software helps me pick up many errors; the computer reads what is actually there, not what it expects to see, and I often hear errors that I haven't seen no many how many times I've read over it. But I still end up missing some.
But no amount of tricks will help you find errors due to ignorance. Unless you are especially skilled in this area, some ignorance in grammar and spelling is likely. And then there are very simple things, like my example of "lounge": all the people close to me use "lounge" the same way I do (as a piece of furniture, and as a room), it took outside help to highlight this as something likely to confuse a wider audience. The point being that we all need help, as much of it as we can get.
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