I had to learn that the hard way, but with a comic/manga idea I used to have.

Long story short: I worked way too long on an idea (almost 10 years), all while my taste etc. changed. It would have been way too hard to get it working after a while without a complete revamp of the whole idea, so I ditched it completely, maybe reuse elements and character concepts in other things, including video games (yes, they're easier to make, unless your comic's artstyle is stickmen figures).