Writing believable characters is a challenge. On the one hand, you'll get someone telling you how much your character resonates with them, and on the other, a callous dismissal with extra emphasis on your lack of character development skills. It doesn't matter how long you've been writing or how many years of character development you have behind you, this confusing response happens to us all.
The trick to getting past this, and eventually receiving fewer and fewer negative comments about your characters, is to take a look at the people closest to you. Friends, family, neighbors, even the strangers you pass by every day on the commute to work or school. Watch them, pay attention to the idiosyncrasies of their movements, the gestures they make, and their own unique lexicon when they talk. Observing people expands your knowledge base and gives you ample material to draw from when developing your characters.
Another powerful tool is to think about the ordinary events and conversations you've had with others. The littlest moments often translate into core components of a personality. Watching the rhythmic motion of your grandmother rolling out a pie crust, and noting her facial expression or the number of rolls before she switches directions, for example. Maybe she huffs a little, or maybe she likes to stop and address you directly to make sure you're understanding her point.Hands on experience is also highly valuable. Growing up, I was my dad's little helper in the garage. I spent as much time crawling around greasy engines and delivering tools as I did playing video games or with My Little Ponies. Giving your characters small personalized details is often more effective than the overarching role they serve in your stories. The quirks can be anything and come from anywhere, just as long as they demonstrate a character's humanity.The next time you sit down to work on character development, think about the little things that make a person tick, and build on that until the concept comes to life.