How secure is security?

In the last few weeks I have accidently left a small bottle of water in my briefcase, a couple of times. In both cases TSA did not see, or at least did not react, to this "contraband". While the bottle is small, it is most certainly larger than the 3 oz limit. I understand that something like this might be missed once, but twice in a relatively short period? Ooops!

So is this an oversight, or just TSA being nice to me?