The difference between “well done” and “congratulations”?

You say “well done” and “congratulations” when someone achieves something or has good news, and they can be used interchangeably in some situations, like someone passing their driving test or getting into college. However I’ve noticed there are some situations where saying “congratulations” is appropriate, but saying “well done” sounds weird. For example, saying “well done” to a woman for getting pregnant doesn’t sound right. Or saying “well done” to people who got married. Or saying it to someone who won the lottery. I was thinking it was because “well done” is more appropriate for situations based mostly on working very hard and where the outcome is within your control, such as exams, a driving test etc. Whereas “congratulations” can be for luck based achievements, like winning the lottery or getting pregnant. Or for personal choices that don’t particularly involve hard work to achieve, like choosing to get married, getting pregnant. Interested in other people’s thoughts, or more examples! I accidentally said “well done” when someone announced their pregnancy and then corrected it to “congratulations”.