What makes a character so lovable, in my opinion, are his or her quirks and habits. The finer details about a character's personality really sharpen the realism aspect of a character and bring them to life. A story is just like a drawing. If you add more detail to a painting, it becomes more realistic. You can easily add more realism to a character by giving him or her some quirks and habits.

Adding these quirks and habits onto a character is easily my favorite part! You might not notice the miraculous change at first, but your readers know and it's often these finer details that they notice and comment on.

If you're confused about what I mean, let me give you some more of my stupid examples. Naruto has an unhealthy obsession with ramen. The Joker from Batman (the one played by the brilliant Heath Ledger) had an odd quirk of his lips and slurring his words together. You could even say his whole personality was a quirk. Even some K-Pop idols have quirks that make them so endearing. Sehun from Exo-K has a lisp. Myungsoo from Infinite collects plaid shirts. Yunho from TVXQ has nice s when he pushes his pecs together. 

You get my point. There's a reason why fans give their favorite idols nicknames, like Key from SHINee as the 'diva' and whatnot. It's because these people have character and quirks, so it's only natural for fictional characters to have them, too.

Your character's quirk can also be a flaw he or she has, as mentioned in chapter one. It can be a compulsive habit or something odd that's noticeable.

Details matter.

Consider details the icing on top of your cake, and all the other finer details the decorations. Most "original" characters on AFF would make horrible, tasteless cakes because they lack the icing on top. Go crazy with the smaller details because they just help bring your character to life.

Give them a speech impediment. Give them an unhealthy obsession with the color red. Make them have a nasty habit of biting their nails or chewing the skin off of their thumb. Maybe they're scared of dogs? Maybe they're lactose-intolerant? Maybe they start hiccuping when they're nervous? The more, the better!

Let's compare a girl with no quirks and habits with a girl with one:

Before: "Ah, this is really delicious!" she ate happily.

After: "This ith really delithus," she mumbled between loud chews, dipping her french fries in more chili, scarfing them down like ammunition and the sauce off of her fingers. A loud burp followed, but she showed no shame as she held out her empty plate, rattling it. "More."

So, this girl has a really, really big appetite, but you see how much depth one little quirk can add to a character?

I have no idea if this relates at all to the subject we're discussing, but I've seen a quote that said something along the lines of "A writer never forgets the small details. A writer may forget anniversary dates, but he will never forget what dress you wore the day he met you." With that in mind, a writer shouldn't forget to add details, especially onto a character that's supposed to convey a certain level of realism.

Realism. Let's cover that next.