well... in MOST situations those that were kicked out following SULE II were already sort of on the bubble. The one candidate we had who was OK until the week 9 boards was kicked out for an integrity violation. But to answer your question charger- no, one bad day or one bad event won't get you kicked out, unless it involves you doing something extremely stupid (i.e. we had a candidate get kicked out for going outside to try and use a payphone during firewatch!).
For the most part though, the people who were kicked out after SULE II were kicked out because SULE II was their last chance to perform, and they didn't.
As far as what the instructors are looking for when it comes to leadership- I think Farkle's advice above certainly rings true- they are looking for confidence, and a good attitude. Also, one thing that seems to save you all the time is PT. If you can run a 300 PFT, life is alot easier, and barring an integrity violation you would have to be a very nasty candidate to get kicked out. Personally, PT was by far my worst aspect, and even though I was actually good at other forms leadership, the fact that I was weak at PT made me a target for the Sgt. Instructors when they were in need of one.
The constant factor that leadership seems to boil down to though is confidence. Work on speaking confidently, and remember to have a good attitude, especially when you are in a leadership position.
In addition to this, as a blanket statement, don't tell a lie for those 10 weeks. Not that there is an abundance of opportunities to tell lies, but an integrity violation is a stupid and avoidable way to get kicked out.