Need for financing/ability to generate cash flow. If a lot of money is required to start testing the concept, either because costs are high or because it will take a while to become cash flow positive, financing will be required either from founders or investors. If you don’t have any existing relationships to investors, or at least close connections, that’s, another time suck and risk factor. It’s certainly surmountable though if you’re good. Raising money, while glorified in the media, does have downsides. For example, you can lose some control over your business and you have to give up equity (and therefore upside). The more cash you need at the start, when your valuation is the lowest, the more equity you will have to give up.