I love my dog. Dogs were the first species to be domesticated.
Is your dog friendly?  Are most dogs friendly?
Yes very friendly. Their association with humans have made dogs very attuned to human behavior.
I wonder why other similar animals like wolves can't be domesticated?
There is Intra hybridization among wolves and dogs because their species are so similar, and genetically very close. 
If you cross a dog with a wolf, will the offspring be domesticated naturally?
Not sure. but such hybridization has been detected in many populations in Europe and North America. 
Perhaps the hybrids are a good thing so the species does not decline thru inbreeding.
can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of said mechanisms.
Inbreeding can result in inbreeding depression, which is the reduction of fitness of a given population due to inbreeding. Inbreeding depression occurs via appearance of disadvantageous traits due the pairing of deleterious recessive alleles in a mating pair’s progeny. When two related individuals mate, the probability of deleterious recessive alleles pairing in the resulting offspring is higher as compared to when non-
in the genome. The same process may also apply to other domesticated animals.
In 2014, a whole genome study of the DNA differences between wolves and dogs found that dogs did not show a reduced fear response but did show greater synaptic plasticity. Synaptic plasticity is widely believed to be the cellular correlate of learning and memory, and this change may have altered the learning and memory abilities of dogs in comparison to wolves.
Dog domestication Positive selection Behavior.
Unlike other domestic species which were primarily selected for production-related traits