The line between unhealthily low self-esteem and selfish egotist is actually quite thin, and it makes it quite a tricky balance to strike. In fact, you will note that most people who operate as egotists have an almost non-existent self-esteem. The reason for this is, to cope with self-esteem issues, some people will latch onto an inflated self-image.
I am actually speaking out of experience on this, being someone who has struggled with chronic low self-esteem, and even self-hatred, and who has "self-medicated" with egotism in my teenage years. I know both extremes all too well. In this state, while it is hard to generate healthy positive messages, it is even harder to generate healthy negative messages (such as "I made a mistake" or "I don't know this subject"); instead, we generate destructive negative messages.
Remember - I am wholly supportive of the tips you provide. Building a positive self-image is a critical half of dealing with this problem. Yet being able to have a healthy recognition of mistakes and areas of weakness are the other half.
In the end, "imposter syndrome" is simply an automatic reminder that we haven't arrived yet ("I am not a true coder until I know X."). Its destructive tendency comes from it running out of control, ungoverned by a recognition of what we currently know and can do ("But I am still a coder because I can do X."). When controlled, it keeps us ever reaching for the next goal, continually seeking to grow and improve.
This is why I say that a controlled case of "imposter syndrome" is actually helpful when dealing with either low self-esteem or egotism (again, flip sides of the same coin). It serves as a set of brakes against over-inflated ego. This is actually more important than it sounds; overcompensating with an unrealistically positive self image sets one up for a dangerous letdown. As soon as the person with low self-esteem is reminded of a weakness or flaw, they come crashing back to earth in a bad way, and wind up LOWER than before.
To put it another way, controlled "imposter syndrome" acts as a cap on our self-image inflation. By "controlled", I mean that we use the imposter syndrome's negative-message-generation, and keep it FIRMLY in check with the positive messages we tell ourselves. This mutual check-and-balance keeps us centered, to where we can safely say things like "I made a mistake, and I am intelligent, so I can learn from it."
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