Back when I sold makeup (on commission), my sales manager once told me, "Sales is great - one minute, you can be totally down in the dumps, and then you sell a $15 mascara, and suddenly you are on top of the world!"
She wasn't wrong. Sales can be a roller-coaster of emotions. Closing a customer feels AMAZING, but the feeling is fleeting. It's a quick high, and then a few days (or even hours) later, you are looking at your pipeline in despair, wondering where that next sale is going to come from.
That's why, when I'm teaching sales, or talking to my own sales teams, I always tell them that the single most important skill you can develop as a salesperson is emotional maturity. In order to be successful in sales, long-term, you have to smooth out those peaks and valleys. The highs can't be as high, but you can't sink so low on the lows, either. If you don't have that maturity, sales becomes an untenable career, with too much emotional fatigue.
(If only that lesson were as easy to learn as it were to teach.)