Almost a year ago I did some analysis on this. It turned out that for a 20% schematic the 90th percentile of trials is at 10.5 rolls, and the 98th is around 20. In other words, 1 out of 10 times it will take you more than 10 rolls to succeed, and about 1 in 50 times (actually, it was 1 in 45), it will take you 20 or more.

If you roll the dice a million times, you will almost always find at least one streak of > 50 failures, and it's about 50/50 that you'll find one taking over 60.