There's two sides to people (well, there's several layers, but let's look at these two sides specifically)- a selfish side and a selfless side. I believe that we were born with both sides, though not all of us keep both.
Both sides have an equal chance when we start out in life, but in nearly everyone one side always becomes more dominant than the other. Which side will win is ultimately up to us, though.
Whether we become more of a selfish person or a selfless person depends on which side gets nurtured more. As time goes on, if we only nurture one side the other one tends to fade quickly.
I believe that everyone has selfishness and selflessness in them, and I believe that we need some of both. I think the selfless side should be the dominant side, but there are times when we should put ourselves first. Knowing when is an appropriate time to be selfish is hugely important.
Personally, I want to start nurturing my selfless side more. Sometimes I don't always know how to help or contribute, but I try. With time, I'll get better at recognizing when a person can use my help. I think that being selfless more often than not is an important part to finding true, lasting success. Giving kindness will only bring it back to you again and again.
Many of us say that we'll be more generous when we "get there" and have money to burn. But if we can't give when we have a little, I don't think we'll want to give when we have a lot. Giving doesn't have to be monetary- it can be time, items you already have, emotional support, or skills. I think we need to start looking out more for each other. If you give, you will receive.