Łukasz about Kuba in his book.

I know Kuba for eight-nine years. We first met in the Poland youth team. Kuba was playing in KS Częstochowa in the fourth division, and I played in Gwarek Zabrze. We started to get along. We were in Switzerland at the European Championships for U19, and although Kuba was sitting on the bench, we were going out together between the trainings. To get coffee or tea. I remember that then Jurek visited him with family, with cousins. Later Kuba was in the same dormitory as me. We were only saying “hi” to eachother. He was in Górnik Zabrze for a very short time. He returned to Częstochowa and moved to Wisła Kraków. Then his career has been developing rapidly. He came out of nowhere and went straight to the starting eleven.
We have become friends during national team training camps. And friendship blossomed when I moved to Dortmund. Our daughters are nearly the same age. We understand each other very well, and I think you can see it well on the pitch. I believe it will stay like this. We will both remember Champions League Final London 2013 BVB-Bayern Munich for a lifetime.
As I stood on the pitch, you could see tears in my eyes, because I realized that I spent so much to get to the finals, and failed to win. I knew that over the next six months I will not play. I think Kuba also had tears in his eyes.
We come from Śląsk. Kuba doesn’t like it when I say this, because Częstochowa was previously a separate province and as I say that he is from Śląsk he gets frustrated. 

I don’t play Heroes anymore like him. Kuba is exaggerating when it comes to computer games. He taught me to play dice, on his rules (laughs). When we were together on vacations in Sardinia, loser’s punishment was to do push-ups or entry into a cold pool.
I trust him very much, which is important to me, because it’s not easy to get my trust.
I don’t have many friends. Two or three from school. I was educated that if I get kindness from somesome, I try to give it back. I think it works in our relations.
I also have good contact with his brother. We like to talk, laugh. We hit each other in the right place at the right time. Our families like each other too, we’re hanging out.
I know how hard his mother’s subject is for him. We had this conversation, I teased my mother and Kuba told me: respect your mother, because it is a blessing. Then I realised how much he missed his mother.
I know this story, but not with all the details. I know what happened after that with his father. I tried not to exert pressure on Kuba to tell me about it. I thought that if there will come a time and place to talk about it, we will.
My parents have only good things to say about Kuba. They like his sense of humor. My mom likes to joke with him.
Kuba insanely likes competition. It doesn’t matter in what and what for, he always have to be the best. Recently we bought remote-controlled cars. We talked about them and we decided that we would go to buy them. We drove them in Kuba’s garden. We disappeared for five hours. It was a draw. We did track, you had to get to the destination and return as soon as possible. We raced. The technique was important. At the beginning I was winning. Later Kuba took the lead, we played to ten races. Finally I said: But I have to go home (laughs). If he wins the next game, then there would be a tie. I dragged playing time as I could and I could see that he was frustrated, because he doesn’t like something like that.
Kuba’s injury in the match against FC Augsburg was a very hard moment for me. I saw how it happened. I was on the bench and saw him holding his knee. Then I just wanted to know if it’s twisted. I asked him and he replied that it is. I had such an impulse that I stroked him on the head. (To journalist) You saw that. When I returned to the bench, I could not believe what had happened. I don’t remember the first half of the match and what has happened on the pitch. These are painful things.
Kuba now has a hard time because when he was coming out of the injury, he tore a muscle. He was devastated, I visited him the next day and I saw how overwhelmed he was.
I told him not to worry. This is not cool, but it happened. But I saw that what I say to him was just like water off a duck’s back.
Kuba have a short temper. He is more impatient than I am. Everything must be here and now and the end. He’ll stand his ground. I’m like this too, but not on this scale.
If we argue, it is only for a moment. I remember some champions league game, Kuba threw the ball and I shouted for him to set up a little differently, and he said: What the fuck do you want, I play football. I thought about it: I don’t say this to you to spoil your mood, I want to help you.
I try to be with him in difficult moments for him. We’re going everywhere together, and since his injury I try to visit him more often.
After the Poland-Germany game on the national stadium I saw Kuba talking to Hummels and I had the impression that he was very sorry that he could not play with us. I asked: Why did you not come to us to say hi? He replied: I don’t want to disturb. I asked: What are you talking about? I shoved him to the locker room. It hurts him how he’s treated in Poland.