Everything we do is in my opinion already ment to happen. We might feel like we have control of our lives but i don't think that's the case. God planned out everything that's supposed to happen in our lives. Its all planned out and crafted. So why be a existentialist? why should it matter?
Even the struggles that we have in our lives was ment to happen and cant be avoided. sometimes we can have presentiment of upcoming struggles but Its just fate. even the way you deal with them is fate. so when people beat themselves up about the way they handled a certain situation i wonder if they know it wasn't their fault. they had no control over it.
Gregor's didn't have any control of the struggles he experienced with is sister, mother and father. He didn't choose to become a roach. "Gregor was so exasperated when she began addressing him again that he ran at her, as if to attack her, although slowly and feebly enough." Gregor's greatest struggle was with his sister. He wanted to be there for her and talk to her. He just wanted everything to go back to normal again.
Even though everything we do is fate. We still have to keep in mind that there is an after life. Nobody knows where or when we're going to die. We haven't actually experienced it. we just have beliefs , some of them stronger than others. Whether you believe in life after death, reincarnation, or neither, death crosses our minds quite often.