Some years ago, we were approached by a local business looking to change accountants (in order to try and lower their fee, primarily).
We had a look at their accounts with them. They'd made losses in their first couple of years of trading. We asked about the numbers, and the scope there was to improve them. How high could the sales realistically get? Could the margin they made on the things they sold be improved, by selling at a higher price or buying at a lower one. What was the realistic scope for trimming overheads without undermining the business.
We concluded with them that as things stood, the best case scenario would mean that they went from losing £50,000 a year to losing £10,000 a year. They'd effectively created a business where the best case scenario was that they'd lose money, and the worst case scenario was that they'd quickly burn through their life savings. That's what can happen if you begin from a position of wanting to go into a business in an area you're passionate about, with no immediate pressure to create profits and an income. If you start the other way round, from the position of wanting or needing a certain amount of income, and work back from that to try and create a model that delivers it, you're more likely to end up happy.
They weren't really ready to hear that though, and they went with a cheaper accountant.