In finding a partner how much did the ‘Key into the lock’ principle operate for you or should operate for all couples? i.e. If you admitted to a weakness then you look for someone of strengths in that area and vice versa. There are obvious physical examples of this like looking for someone with a womb, but there are other physical considerations like those of Jack Sprat and his wife. What about others - emotional, cultural, religious? Are there any other principles besides “ Sheer compatibility” that operate. NB I have not looked for a partner for quite a few years and have no plans to do so but have been thinking about the foundations of my relationships e.g I knew my wife would be good with young children because she was a young age (kindergarten) teacher whilst I was a higher school teacher.