The 33-year-old, who won the 2006 World Cup for his country in partnership with former world number one Bernhard Langer, has won two European Tour events in the last 12 months and is confident of doing well at this week's Open.
"Since the birth of my daughter 2-1/2 years ago I take golf much more seriously," the pony-tailed Siem told Reuters in an interview. "I used to throw away so many good results because of my emotions.
"I think positive emotions are good to show. The spectators like it, they give me high-fives, and in the U.S. they really like me because of that.
"On the other side I'm doing a lot better with the negative emotions. I'm trying not to let them grow too much and accept I'm not a robot and that I'm allowed to make bad golf shots and get bad bounces and not let them ruin my whole round."
Siem is up to 60th in the world rankings after winning the 2012 French Open and this year's Trophee Hassan in Morocco.
That represents something of a career turnaround for a player who once had a group of children in tears due to his on-course antics.
"It was at one of my home tournaments in Cologne about eight years ago," said Siem. "It was my last hole and I was about to miss the cut and broke my driver over my knee.
"There were a lot of kids watching and they started to cry. I thought to myself, 'That's the last time I do that'. I went up to the kids, gave them a hug and said sorry.
"I suddenly realised how much impact our behaviour has on kids. I will never behave badly like that in front of them again.
"That was the worst incident and I nearly had tears in my eyes because I saw the little ones crying. After that I said I'd try to be an idol from now on and that was a turning point for me, big time."
Siem, who will be making only his third appearance at the Open this week, takes his golf much more seriously these days.
"I love the game," he explained. "I'm 33 now, I'm not the youngest out here and I'm not the oldest but I've still got a lot to learn from golf and life in general.
"I've been working a lot harder since my daughter was born. It was like someone turned the light switch on in my life and I thought, 'Right I have to look after my wife and my kid now'.
"I never used to think about money, I never had a house, I lived in apartments, but since my wife became pregnant I decided to take life more seriously," said Siem who is a golf ambassador for Mercedes-Benz, an official patron of the Open.
"I go to the gym in the morning, work hard in the afternoon, work again in the gym in the evening and I think that makes me a better golfer."
Langer is the complete antitheses of his compatriot - calm, sanguine and methodical - and although Siem said he could not describe the 55-year-old as his best friend, it is clear the veteran is an inspiration.
"We've not had a lot of contact since the World Cup but then last year I phoned him when I was in Florida and he was in Boca Raton, literally five minutes away," said Siem.
"We both had a week off and I started practising with him. He is so calm and from his whole attitude I learned a lot from him about golf.
"The way he talks, it's so different to others, and it's worth a lot to me, golf-wise and human being-wise," said Siem.
"I went to church with him as well. I hadn't been for a long time and it was a pretty cool experience. He's great, he has so much knowledge and I try to see him as much as I can."
Siem still wears his heart on his sleeve on the course but is keen to point out he is a different man when he is not at work.
"I get so many comments on my Facebook page from people who say that from my reactions it looks like my ball has gone out of bounds or in the water but it's literally two metres from the flag," said the German.
"The reason is that when I don't hit the ball in the centre of the club it feels odd, it doesn't feel right and I'll go 'arrrggghhhh'. It's the perfectionist in me.
"I'm a feel player and when something's wrong with my feel I show it. I know it's wrong and it's not good for my golf but I'm getting a lot better now.
"I've had two top-10 finishes in my last three tournaments and I'm feeling really good going into the Open."
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