The digital advertising expert dropped to all-time lows on Tuesday, despite robust Q2 results. Here's why.Shares of PubMatic (PUBM -20.62%) took a swan dive on Tuesday morning, starting the morning session 33.7% below Monday's closing price. The company reported second-quarter earnings last night with strong results but uninspiring forward guidance.The stock had recovered to a 19.4% drop by 12:50 p.m. ET, but that's still a painful price cut.Beating estimates isn't always enough for Wall StreetThe digital-a ...