I think it is because I see my weaknesses in them and it either shames me or annoys me.
Or when it's your child - it can scare you (or at least it does me).
My son, quite possibly, could be the most stubborn person I've ever met - beside one of my best friends.
I thought I was that (the most stubborn). But they are two people who are even more stubborn than I am. In the case of my friend - it's none of my business really - and I can only advise and then watch it all unfold. But in the case of my son, I used to get crazy with fear when I'd watch him be as immovable as stone on one issue or another.
But now I've learned not to expect either one of them to change his mind once he's made it up. They both have to learn the hard way that determination can be a good thing - but willful or prideful stubborness lands people in deep **** sometimes.
Linkat - I knew someone like that (your husband). If we'd go shopping - I'd say, 'That's pretty,' and when we got home, she'd hand the item to me. She'd have bought the thing. I learned that I'd have to say - 'That's pretty - but I don't want it- I just think it's pretty...' The last time I was home, she gave me this set of windchimes she'd bought on a trip - but I just happened across her outside her house when I was walking - she hadn't known I'd be home, so I knew she hadn't bought the windchimes specifically for me (and I really didn't want them). So I said, 'No, you must have bought these for someone else...you don't have to give me anything- what will you do for the person you really bought them for?' And she opened this bag and showed me that she'd bought THIRTY windchimes (they'd been on sale).
I thought, 'Wow - how does her husband support this habit?' (she doesn't work).
But as a frugal person who does like to indulge when the mood strikes (in music, plants, travel, good food) I don't know if it'd be harder to be married to someone who was a free-spender or stingy- someone who NEVER wanted to or wouldn't allow you to spend anything on anything fun.