Analysis Paralysis. I don't think I have any bigger wasted-time-sink in my life then over analysis/planning/selection.
* Loosing an entire evening trying to find the best library/language/engine/etc for a side project idea, rather then actually getting the idea going.
* Loosing entire days trying to find the best design/structure for a project rather then adding features.
* Loosing hours comparing and reading reviews for trivial purchases.
* Designing and redesigning an idea over and over in my head or on paper, but never getting it started as the design wasn't done/perfect.
* Rewriting a side-project in a new language because it will be faster, more organized, more elegant, etc... rather then actually finishing it and releasing it.
* Waiting for the perfect conditions, weather, time, mood, etc to do something.