FadeToBlack&Gold
8647
Typically it's when the discrepancy in incomes is very large. Happened with my doctor brother/teacher SIL.
This. My SIL has a PhD in genetics and works for the feds. She makes decent, but not great money - could likely be quite a bit more if she had gone private instead of choosing the public sector. My BIL is a stay-at-home dad to their two sons. He does bartend 1-2 nights per week to help them make ends meet, but for the most part he's keeping our nephews (10 and 5, both super-ADHD and likely some degree of ASD) on task/schedule, enforcing their rules, doing the majority of the housework, etc.