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**Rounds**
It is likely that your group means are ordered

Y < X < Z (or the opposite).

The trick to understanding this is to picture a confidence interval around each group mean. You don't actually know the extact location of Y's mean with 100% certainty. You know the best guess of Y's mean and you know the interval around Y's mean with 95% confidence. This idea that you only really have a guess about an interval is what is going to inform your intuition.

It turns out that the intervals that you think might contain Ys mean and Xs means overlap. So you can't really be all that certain they are actually different means (or more precisely "this is insufficient evidence that they are statistically different". Likewise X and Z.

However there is no overlap of these intervals between Y and Z. So this is statistically significant evidence that Z and Y are different.

You essentially don't know whats up with X relative to Y and Z. X could be exactly Y. X could be exactly Z. X could be dead set in the middle. You don't have the statistical signficance to say really with these test and these data.