How can they be so different?

I struggle with this daily with my kids. How can two boys from the same parents be so opposite of each other? At least it keeps our lives interesting. I've started to ask myself this question about dogs too. When I finished my freshman year of college I adopted a pound dog from the local SPCA. He was with us through 7 apartments, 2 children, the adoption of a rescue basset and spent 14 years with us. He passed away in August and we miss his every quirky quality. He was always happy to see you come home. Never stole food from the table or counter. Never jumped on the furniture. Never barked unless necessary to ward off intruders. Never made a mess inside the house even after being left for 14 hours. This basset has a completely opposite demeanor. No "happy to see you" barks and tail wags upon returning home. Messes of pee and poop all over the basement after being left for a couple of hours. Packages of crackers and bagels stolen from the counter and table. Rips in the cushions of our furniture from jumping on and off them when we're not home. He's more friendly with strangers approaching the door than when we come home(not so comforting in our neighborhood). It's not fair to expect the basset to be a perfect dog but it's hard when Sammy was such a good dog. Even after 3 months of not having "old man" around, we haven't gotten used to life without him. The basset misses him too. For 2 years Sam was the alpha dog setting him straight, keeping him in line. We've thought of getting rid of the basset but I can't imagine life without a dog. I've lived with a dog for 32 of 33 years of my life. There's whispers in our house of searching for another dog in the future. Will dogs in our house work better in pairs? The basset would really like to have another partner in crime. It's been pretty easy with 1 dog. No guilty feelings of taking one for a walk and not the other. I guess I'll use the line my parents used with me-"we'll see."