True, and I hope no one thinks it is. So we can conclude that doing bad shows at first is not a strong indicator of whether you have a future as a showman.

I guess I see the quote as being directed at people who are so afraid of doing a bad show that they'll never get in enough practice to do a good show. Or they practice by, say, filming themselves telling jokes in their basement and getting critiques from their friends who will not be too mean to them. In either case, they never get the amount of feedback they would need to become good. For such a person to hear "Yes, you will fail" can be oddly liberating, since it turns failure into something accounted for in their longer-term plans.