Positive thinking is a powerful tool but only if you use it in the right way.
Positive thinking is a wonderful thing, but it can get you into deep trouble. If you're not careful, positive thinking can turn into "magical thinking" where your desire to win overwhelms your ability to perceive what's actually going on.
Nowhere is this more obvious than in sales. Salespeople tend to be positive thinkers, which stands them in good stead when they need the motivation to keep working even when things get tough.
However, it's not unusual for salespeople to become so enamored of an "opportunity" that they fail to read the signs that this customer just isn't going to buy. They think so positively that they end up pursuing dead end deals.
Entrepreneurs have similar failings. Because they're so positive that their product or business strategy will work, they miss opportunities to change it for the better. They let enthusiasm gloss over real problems that make those strategies ineffective.
In both cases, the problem is the same: thinking positively about the wrong thing.
With that in mind, here are some quick rules:
Be positive you'll achieve your goals, but not that your goals will never change.
Be positive you'll do your best, but not that your best will always win.
Be positive you'll overcome obstacles, but not that obstacles don't exist.
Be positive you can help your customers, but not that everyone is a customer.
Be positive you'll make hard decisions, even when it means cutting your losses.
Be positive you'll manage your emotions, but not that you'll never be disappointed.
Treat positivity as part of your tool kit, but not a tool that fits every situation.