2011湖南完形填空一句话的意思

People in communities have slowly been pushed apart through the years, mostly because people simply aren’t taking the time to say a simple “hello.” After considering this phenomenon, I decided I was going to   36   the way I was doing things.

My  37  came one morning when I was in the community library. I passed by a girl who   38 her books out of her locker. Thinking like most that someone else would help her pick them up, I continued my way. However, when I had to   39   because I stupidly forgot my book, I noticed she had just finished packing them up by herself. No one h ad stopped to   40   her.

“OK,” I thought to myself, “this is where I should have changed.”

My best opportunity came a few days later when I saw a man   41  by himself waiting for the library to open, so I sat down next to him and began a  42  . It was difficult to get started, and even when I had to say goodbye, almost every  43  from my new friend had a tone (语气) of doubt in it. And who could blame him?

People aren’t used to making an  44   chat with a stranger. But a change, no matter how  45  it is needed, doesn’t just happen. It takes people like us to make it possible. I  46  you to take a small step out of your comfort zone and try to make someone’s day a little brighter. Together, we can really make society come   47  as a whole.

问：But a change, no matter how desperately it is needed, doesn’t just happen. 为什么要填happen?这句话什么意思?