The Bible says, in Job 5:2, “For wrath kills a foolish man, And envy slays a simple one.”
A German proverb goes, “Envy eats nothing, but its own heart.”
Dr Caroline Leaf, communication pathologist and self-titled cognitive neuroscientist, posted today on her social media feeds, “Jealousy and envy creates damage in the brain … but … celebrating others protects the brain!”
Yes, sometimes envy isn’t good for us. Emotions guide our thought process, and like all emotions that are out of balance, too much envy can cloud our better rational judgement and bias our perception of the world. Thankfully, envy doesn’t literally eat out our hearts or literally cause brain damage.
If anything, envy when experienced in a balanced way can actually improve our brain functioning. According to real cognitive neuroscientists, envy and regret are emotions that help us because they both fulfil the role of effectively evaluating our past actions, which improves our choices in the future. As Coricelli and Rustichini noted, “envy and regret, as well as their positive counterparts, share the common nature that is hypothesized in the functional role explanation: they are affective responses to the counterfactual evaluation of what we could have gotten had we made a different choice. Envy has, like regret, a functional explanation in adaptive learning.” 
When it comes to the human psyche, there is no black or white, good vs evil distinction between different feelings or emotions. B-grade life coaches and slick pseudoscience salespeople dumb down our emotions into a false dichotomy because it helps sell their message (and their books). Every emotion can be either helpful or unhelpful depending on their context in each individual.
As Skinner and Zimmer-Gembeck wrote, “Emotion is integral to all phases of the coping process, from vigilance, detection, and appraisals of threat to action readiness and coordinating responses during stressful encounters. However, adaptive coping does not rely exclusively on positive emotions nor on constant dampening of emotional reactions. In fact, emotions like anger have important adaptive functions, such as readying a person to sweep away an obstacle, as well communicating these intentions to others. Adaptive coping profits from flexible access to a range of genuine emotions as well as the ongoing cooperation of emotions with other components of the action system.” 
If you find your thoughts and feelings tinged by the greenish hue of envy, don’t worry, it’s not necessarily a bad thing. Your heart isn’t going to consume itself and you won’t sustain any brain damage. Use envy or regret as tools of learning, tools to help you evaluate your choices so that you make a better choice next time. Having balanced emotions is the key to learning and growing, coping with whatever obstacles life throws at us.
- Coricelli, G. and Rustichini, A., Counterfactual thinking and emotions: regret and envy learning. Philos Trans R Soc Lond B Biol Sci, 2010. 365(1538): 241-7 doi: 10.1098/rstb.2009.0159
- Skinner, E.A. and Zimmer-Gembeck, M.J., The development of coping. Annu Rev Psychol, 2007. 58: 119-44 doi: 10.1146/annurev.psych.58.110405.085705