Accounting techniques like budgeting, sales projections and financial reporting are supposed to help prevent business failures by giving managers realistic plans to guide their actions and feedback on their progress. In other words, they are supposed to leaven entrepreneurial optimism with green-eye-shaded realism. At least that’s the theory. But when Gavin Cassar , a Wharton accounting professor, tested this idea, he found something troubling: Some accounting tools not only fail to help businesspeople, but may actually lead them astray. In one of his recent studies, forthcoming in Contemporary Accounting Research , Cassar showed that budgeting didn’t help a group of Australian firms accurately forecast their revenues. In a second paper,he found that the preparation of financial projections added to aspiring entrepreneurs’ optimism, leading them to overestimate their subsequent levels of sales and employment.  “It’s been shown in many studies that people are overly optimistic,” Cassar says.…