"Attrition is a group statistic. It doesn't apply to me."
Special forces training is taken by a large number of people - some of these people are just chancing it, hoping they will be able to push through anyway but not really prepared or ready for it. Others, like your brother, are fully prepared. When looking at a base rate, it's important to understand the different divisions inside that base rate and the reasons people drop out.In special training, the reasons people are likely to drop out are because they aren't physically fit enough to cope. This gives your a brother a good indication - he likely knows others of similar fitness to him who passed. The key here is that there isn't much randomness involved - either you are fit enough or you aren't.Startups are a completely different ballgame. The main factors behind dropping out are a complete mystery - team composition, relationships, lucky deals with investors, hitting your marketing in at the same time some other big player pulls out or pitches in - the list is endless and impossible to even fully understand.Basically what I'm trying to get at is that comparing something you have complete control over (special forces training) vs something you don't (a startup's success) is not a great analogy.However you're still correct anyway - the best indicator of whether a startup succeeds is whether or not they try in the first place! So it's always best to try and ignore the baseline.