-Grendel may have led a painful life for several of reasons. Mainly because he was a descendant of Cain. Meaning he was born evil no matter what. Also, people compared him to a beast which made him lack confidence in himself. Last but not least would be because clearly Beowulf came to kill him and that is alot to endure. OR you can word it this way
-One reason Grendel led a painful life is that he was a descendant of Cain. From the beginning he was born out of pure evil. Another reason Grendel may have led a painful life because he was compared to a beast. The motives of this beast was to stop any festivities in Heorot Hall; which caused him to be a primary target
of King Hrothgar. A third reason is the fact that Beowulf came to kill him. Clearly fighting the protagonist is a painful endeavor.
OR you can word it this way
-1. He's a big ugly monster
2. He got his freaking arm ripped off.
3. His Mother is a lot cooler then he ever was
OR you can word it this way
-Well, for one, he was a totally ugly monster. He could also have had mother issues...from what I remember, Grendel's mother was the more powerful monster of the two, as Beowulf had a much harder time defeating her than him. And third, maybe it gets tiring killing people all the time? All that blood and gore can really get you down, I'm sure...