You don’t need to know everything; you need to know everything important. There’s a big difference between the two preceding phrases and it’s where business people and business buyers often get tripped up and/or fall into the analysis-paralysis trap.
In most situations you don’t need to know everything. In my first sales job I remember a fellow employee who wanted to know everything about a company before he called them (this is in the pre-Internet era and information wasn’t as readily available). Because of this he made a lot fewer calls than he should have and didn’t last long.
A business buyer client of mine, in the course of due diligence, said he wanted to find out what each employee did all day long. I simply asked him, why? He didn’t have a good reason, he just thought he should know. I pointed out that the company was doing well, the employees were getting their jobs done and asked what he would do with that information once he had it. He quickly moved on to getting important information.