Past.

 Past is something that you can't change, you can't go back in. Past is something that will make you wish to go back in time and change whatever happened or beg yourself to forget it. 

Past is like, when you hold someone's hand, shaking hands with them. It'll continue to hold you till when you hold it, but once you let it go, it'll let you go too.. 

Even though, your past may have given you some scars that you can't forget, you can't bury or heal them easily. But to live in present you have to do it. Or else it won't let you live in present, work on yourself, and think about future. Thinking about whatever happened earlier..won't change anything it'll just continue to ruin your present which will ruin your future too. 

So it's better to focus on present and work for our bright future. Because maybe, our past wasn't that great...all rainbow and sunshine, but full of rain and thunder, however that doesn't mean, Our future would be the same...there's always the brightest Sunshine after the darkesr hour of dawn. As they say, "Your story may not have such a happy beginning, but that doesn't make you who you are. It is the rest of your story, who you choose to be. 

                                                 - Kung fu Panda"