Phishing is still the number one cause of data breaches. Phishing ranges from the painfully obvious to the nearly impossible to detect. The true strength of phishing is its reliance on human error. Even the most perceptive users can fall victim to one of these highly sophisticated phishes. Spotting phish is a skill that can be taught, and it can be done with a social engineering pen test. There are plenty of resources for those looking to learn how to successfully create and execute their own ethical campaign.
Source: https://threatpost.com/helpsystems-what-is-the-best-defense-against-phishing-attacks/153711/