Amazingly brilliant plot aside, I admire the way Rowling portrayed the characters and the different relationship or magical bonds between them. Some notable ones include the trio's friendship, Harry Potter's mysterious link with Lord Voldermort and the ancient magical bond between Harry Potter and his mother.

Small little people but with spiderweb-like entangling with one another
J K Rowling did an amazing job at establishing the friendship between the trio in the series. For one, the trio were not all agreeable at the start of the series. There was an unmistakable disdain between the the two boys and Hermione due to the glaring dissimilarities between them. Hermione was exceptionally perspicacious and by-the-book while the two boys were hazardous in nature. Yet, as Rowling so aptly wrote, "There are some things you can't share without ending up liking each other, and knocking out a twelve-foot mountain troll is one of them."

"Probably a nose-breaking wrestle with Snape in the dungeons?"
That one similar incident made them realise that they do have a similar sense of loyalty towards people who helped them and this attitudinal similarity enabled them to form a bond with one another. This is due to people's tendency to form relationships with those we perceive to be similar to us. The three of them realised that the values they share may be the same despite differences in their characters. Forming relationships due to this reason can reduce our uncertainties about them, reduce the associated risks in the relationship and serve as a form of social validation.
During later parts of the development of their friendship, one will see that their initial dissimilarities (or complementarities) actually sustained their relationship as they function better together than separately. Each of them had specific characteristics that enabled the trio to survive through many treacherous vicissitudes. Harry's valour motivated the trio to brave the many obstacles, Hermione's brilliance with spells warded off many magical disasters, and Ron's goofy nature was... well... great moral support? Their dependency on one other was exemplified when cracks appeared in their friendship but they soon realise that their bond was an intrinsic part of each other and patched up soon enough.
JK Rowling ingeniously portrayed how similarities and dissimilarities between people can co-exist and, most importantly, build a bond so pure and perennial that it evokes envy among people who yearn true friendship. I believe the series will continue to touch the hearts of many others even after her mortal departure (choy choy choy), becoming an old Classic like Charles Dickens' Great Expectations. It will continue to impart values of courage and loyalty, and teach the future generations of love and friendship.

PS, pictures in this post do not belong to me, click on pictures to reveal credits...