With a drawing or a song, I can ask, how good is it? Or I can ask, how good am I at doing this? These are usually the wrong questions, though they are different from each other. Am I a good songwriter? I don't really care, because nothing is of consequence in the answer. Is a song good? If I like it myself, that is enough for me. If you like it, even better. I could be a good songwriter and write a song that's not as good as another, etc... Tons of people hang up their art works in coffee shops around town. Some is fantastically good, some is not, but it shouldn't really matter to the artist what I think.
I do things seriously, whether I am an amateur at any particular thing. In fact, I have decided to pursue hobbies seriously rather than thinking of them as something I am bad or good at. Thinking you are bad at something is every bit as much of an ego move as thinking you are good. To invest serious effort simply means that you think of the activity itself as more significant than your ego investment in it.
Shame is a factor. For example, I have played piano in the student union for anyone walking by. I don't have to feel embarrassed any more, because I realized that nobody really cares how well I play, if they are listening at all in the first place.
It's the same with everything I do, except that I am a professional literary critic slash academic, so there I have criteria which are common to the field of inquiry itself. They are commonly held, and I have my own preferences on top of that, my own quirks.
If you confuse "how good am I" with "how good is it" you will be in trouble. Suppose you write a paper for school in two hours. The paper might not be good, yet, because it is not really done yet. You might be good at writing papers, but you haven't spent enough time with this one yet. If you spend endless time and still can't make the paper good, it means you aren't good at it... yet. You need to write many papers in order to learn how to do it. The ego is mostly a hindrance: you need basic confidence, but you need to be able to look at a piece of work outside of yourself and see what needs to be fixed.