Hello. This question is about the graphical novel "Maus", however, you did not put the passage to which this question refers, so my answer below refers to the complete work. I hope it helps you.
Answer and Explanation:
The saying shown above applies to the whole story of Vladek, from his marriage to his survival in the holocaust and reunion with his wife.
At the beginning of the story, we can see that Vladek did not wait for luck to fall into his hands, but it was after a good job and an advantageous marriage for him. This gave Vladek a life without needs and with extreme comfort, but all of this was achieved with his effort and not with luck.
Vladek also managed to spend a lot of time without being caught by the Nazis, as he was proactive in finding hiding places that would keep him and his wife safe, even the moment of their capture is made during an attempt by Vladek to flee to a country free from Nazism that , although it did not work, it is an example of his proactivity and the ability to make his own luck.
However, the moment when this saying becomes more evident when Vladek is in a concentration camp and uses all his wits to make this moment less deadly. He uses every opportunity he has. He teaches English to the concentration camp leader to have some privileges like food and clothing and learns a new profession to stay in a less depressing and exploitative sector of the concentration camp.