If you want to feel like the world is crazy and that everything is stacked against you, try looking for a dog. You can do so much searching and get nothing in return but discouragement.
There is a reason for this: most dogs simply don't fit reality for most people. Most dog species were developed to perform some function that no longer matters much: retrieving dead ducks from a pond, protecting a herd of sheep from wolves in the mountains, chasing rodents away from the corn crib, pulling a dog sled in the Yukon, hunting wild boars, patrolling the barbed wire perimeters of POW camps, etc.
What do people need today? They need a small dog that doesn't shed too much, and loves being a good companion. But those are the dogs that are instantly adopted by somebody else, so you never get the chance.
And what is left to choose from? Losers.
There are several mistakes I must avoid when choosing a dog.
1. Don't choose a dog with your eyeballs. Choose behavior, not appearance.
2. Go ahead and admire people who are virtually "Mother Theresas" when it comes to canine basket cases. But that doesn't mean that I should try to be so saintly. It is no small achievement to tolerate imperfection in a basically good dog. It is not realistic to aspire to absolutely unconditional affection.
3. Avoid trendy popular dogs. These days, doodles are all the rage. They are over-priced. I am suspicious of charlatans who breed these dogs and try to sell them for top dollar on Craigslist.
4. Stay flexible. Don't lock onto an image of the perfect dog, and then demand that any real dog must live up to that ideal.
Think of a breed of dog statistically, that is, as a bell-shaped curve. The midpoint of the curve for Breed X can be distinguished from the midpoint of the curve for Breed Y, but an individual dog can still vary widely from the average of its own breed.
5. Don't take information literally. There is a lot of BS offered in books or on the internet or from the animal shelters.
There are probably more mistakes to avoid, but these are the ones that come to mind right now.