IMO the two reasons for failure are pushing too hard and drilling tempered glass. It really is more grinding than drilling. Also, always check for tempered glass no matter what you are told. Putting a folded towel (or comparable) below the hole is good practice in order to catch the round piece of glass that falls when you finish drilling. Additionally, sometimes an overflow will come with a drilling template. I have also created a jig using a small square piece of plywood and a hole saw to drill the appropriate sized hole then clamp the jig into place. Out of the roughly 30 tanks that I have attempted to drill, I have messed up three - the second tank because I didn’t understand the concept of grinding, the 11th or 12th because I got overconfident and tried to rush, and then another one that was tempered and I found out the hard way. My recommendation to someone wanting to learn is to get a 10g tank (or similar cheep/free used tank) to use as practice and then drill a bunch of holes in it. Two things to keep in mind - (1) go slow with light pressure (just enough to make sure you are actually grinding - you should be able to head the difference) and, (2) use even less pressure when you are almost through (you will learn what that feels like). It is scary - I still get a little nervous, but IMO that helps with concentration. Good luck if you do decide to try it!