Having sisu means that someone is unyielding and determined. He/she has endurance and resilience. That’s what the Finns are known for and very proud of. Sisu can be connected with sports. Especially cross-country skiing and ski jump where Finns have succeeded.
Finnish people need their own personal space. It’s not okay to go and hug or kiss a stranger or even an acquaintance. I guess almost everyone is familiar with a picture from a Finnish bus stop where people are standing a meter from each other just because they need their own space. They might do that even if it’s raining and everyone won’t fit under the shelter. Or perhaps it’s just a bit exaggerated.
Finnish people don’t mind being silent. Sometimes it’s even desirable. When you’re driving a car in a bright summer night and listening good songs. Or when you’re enjoying the heat of the sauna. You seldom hear strangers talking to each other in an elevator or in a bus. First foreigners might find this behavior strange and disturbing but during time they might start to enjoy it. Enjoy those lovely moments that doesn’t need to filled with small talk.