IMHO the issue is that society tells couples that 1 is the ideal outcome, creating plenty of 2s who believe they will eventually become 1s if they just keep try

IMHO the issue is that society tells couples that 1 is the ideal outcome, creating plenty of 2s who believe they will eventually become 1s if they just keep trying. Some of those couples might be happier as 3s. I believe both 1 and 3 are preferable to 2 or 4, so I don't find this trope particularly helpful. It doesn't really matter if 1 is best or not, since it's not going to be possible for everyone.