I've always been a believer in positive thinking. When I get started on a project, I hope everything will go well and I expect things to work out. Most people feel the same, and that's a problem.
A friend told me about how he went into business with a partner. They planned to bid on jobs, do the work, then get paid. This worked for a while, but then there was a problem. The problem was that they bid a job at a fixed rate, but the work turned out to be more than was expected.
They could respond to this problem by either reneging on the deal, or incurring additional expense to finish the work. They disagreed. As a result the partnership and the friendship ended.
Murphy's Law was named after an engineer named Ed Murphy. He noticed that when it was wired backwards it would be ruined, but was annoyed when he discovered someone had wired up 20 consecutive gauges backwards. He then had the idea that the strain gauge could be made so that it was physically impossible to wire them backwards.
Because Murphy recognized that Failure was an option, he could think through ways to make it harder to fail.
When you sign up for a Kickstarter project, you have to enumerate the risks that you foresee. Failure is not an option, it is many options. And you have to write them all down.
You can think positive, but if you do, you may overlook the fact that a supplier might raise prices, someone might get sick, you might underestimate the cost of shipping, or something else. When enumerating risks, you want to think defensively.
Had my friend considered the possibility that he'd disagree with his partner and planned for that disagreement up front, he could have avoided the partnership and kept a friend, or he could have agreed up front how they'd work it out. If they'd considered the possibility that the work could exceed estimates, they'd put in place contingencies to get paid more or to back out of the contract gracefully.
There is a difference between planning to fail and planning for failure. Sometimes success comes after overcoming one or more reversals. You should expect to succeed and you should expect to use one or more of the contingencies you've put in place for the parts that go wrong.