I've found it nearly impossible to predict failures. We try to keep our robot as modular as possible, and try not to burry fasteners and mechanisms so they are hard to maintain. For example, our elevator & roller assembly is removable with just 4 bolts and a few wires.
Make sub-assemblies easy to maintain. For example, our first rollers had 1/4" bolts threaded into both ends. Changing a roller or a belt would take 10 minutes. Now we have a 1/4" bronze bushing in each roller, riding on a 1/4" rod, with collars. Now to maintain the roller, just pop a collar and pull out the rod.
Read: FRC Suggestions, Rev A - the document formally known as FRC Guidelines, Tips, and Good Practices
http://www.usfirst.org/uploadedFiles...%20Rev%20A.pdf
Make bumpers easily removable.
Keep the robot Simple (KISS) and it will be reliable.
Chains will stretch/break-in. Allow for a tensioning system on any chains longer that a few inches.