Board Thread:LOC General Discussion/@comment-216.125.251.254-20130204164334/@comment-5662406-20130529131321

Don't know about it being totally random, I have enhanced many cards to skill 10 and have only had it ever fail 1 time when going 90% or better. Maybe it is a crap shoot for  under 90%, but I would rather assure myself the Skill increase vs wasting cards at a lower %.

The Skillspage breaks down the basic % very well, but for above Skill 5, you will need to you higher skilled rares as suggested above.

Good luck ^_^