What is the central message in Forrest Gump?

A possible central message for Forest Gump could be, "When life throws you lemons, make lemonade". In the story, Forest often repeated the saying, "My mom always said, 'Life is like a box of chocolates. You never know what you're gonna get.'" No matter what came his way in life, he overcame by staying positive and making the most of each situation. Throughout his life he endured a variety of situations - some highlights and some trials. In situations where other people would have caved in or would have become depressed, he remained strong, "made lemonade" and encouraged others to do the same in spite of his short-comings. He proved that any dream can be accomplished if you just believe.

One possible central message of the story could be to never give up. From birth, Forrest is handicapped both mentally and physically; however, he never lets that stand in the way of him pursuing his dreams or doing the job that he has been told to do. You could call it a hardworking spirit or perseverance, but the important thing is that Forrest refuses to give up on himself or anybody else. It's why Lieutenant Dan and Jenny are constantly being looked after by Forrest.
I think another central message of the story could be to love unconditionally. This does sort of tie in with the never-give-up attitude, but Forrest is a living example of what it means to love your fellow human. That's easy to do when the other person loves you back, but there are many times when people treat Forrest in horrible ways; however, Forrest never reciprocates those attitudes and actions. He treats everybody the way that he would like to be treated.
Finally, I think another possible central message is that a person should always make the best of any given situation. Forrest does this by always doing his best no matter the situation. Situations may change, but Forrest has a great ability to "roll with it" no matter what. He even tells people about this particular attitude of his when he says, "Life is like a box of chocolates. You never know what you're gonna get."