go to show
To prove, demonstrate, or indicate that something is true. Used especially in the phrase "just goes to show." Their success just goes to show that you can't underestimate the power of good marketing. My grandfather's pocket watch still runs perfectly after all these years, which goes to show the level of craftsmanship put into it.
(It) just goes to show (you) (something).
That incident or story has an important moral or message. Tom: The tax people finally caught up with Henry. Sally: See! It just goes to show. Angry at the young grocery clerk, Sally muttered, "Young people. They expect too much. It just goes to show you how society has broken down."