When entrepreneurs say that they learnt the hard way, they mean two things. They learnt that you need to be around long enough to really understand what business is all about and secondly that you should never invest a penny until you have identified a clear target market for your product.
This doesn't mean that you shouldn't follow your heart, it just means you need to first start with market research.
We can all be passionate about this or that product, but how much more passionate are you when you are really in touch with your market? When you know how it thinks, what it looks like, how it is motivated and what it believes in and wants for the future.
You need to see, smell, touch, hear and taste your audience before you can truly cater for their every desire.
Don't start a business until you understand who you will be dealing with. Its all very obvious really, but 9 out of 10 business that fail - start with no Market Research.