Not thinking about it is not the problem. A lack of domain knowledge is. If you don't know how payrolling actually works in practice, no amount of thinking will make you come up with the right solution. The real pitfall here, and the downfall of many startups, is thinking you can understand the domain merely by thinking about it. Engineers can usually think pretty well and can solve many problems in that way. It's crucial to realize not everything can be solved by thinking about it.