Here's the counter example of what happens if you DO get tired of your side projects one way or another, not that there is anything wrong with that.

http://sideprojectors.com

(disclaimer - I maintain the site)

Based on my experience of running the site over a year now, there is nothing wrong with side projects that do not become "success" (whatever the definition of your success may be). The most important part is the building it and shipping that v1.0 (or v0.1.. whatever).