Dude, I KNOW how to make variations of a theme, how to make interesting, transposition, variation, there are many techniques. You mentioned a lot of ways. I know them. You didnt understand me. I DO NOT WANT to make a theme interesting when I get bored of it. When I get bored of something I dont want to deal with it. Let us say I start a March like that, than my band we play for example the "Phil Collins Collection", and than I'm not interested in writing a March anymore, now I want to write something popular. I know how to develop a theme, if you dont believe me listen to my Twinkle song. Its a five minute piece based on "Twinkle,twinkle", many variations, transposition, different context/styles. The problem isnt that I cant develop themes, the problem is I dont want to develop and dont want to deal with something that I get bored. so I stop writing it.
Thanks for your comment anyway! :D
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EDIT: Most of times I dont develop a theme not just because I get bored of it, most of times I'm afraid of that the listener will get bored of from the many variations. I dont like when something get predictable. For example a Disco "music" is very predicatble: Tucc--tucc-ttuccc....I hate when a music is predictable, but you're right that doesnt mean that someone dont have to develop the theme.
EDIT 2: I have so much different ideas, that I cant use in the same time, so when I start to write something I easily get bored since I have other 10000 ideas that I want to use just these ideas maybe dont fit with the previous one so I start a new work...and unfortunatelly thats why I rarely finish my pieces. I finish only the most interesting ones.