Why does life looks like a bowl?

Some people say that life is a bowl of happiness and sadness, both may happen at any time of life but for some people life is only a bowl that contains sadness , sorrow and depression. You don’t believe it ,I am myself an example of such people,let me tell you what happened to me . 

It was late evening , I was excited for my birthday, presents , cake and other stuff. I was about to be 13 years old , a teenager offcorss!! Well this birthday turned out to be the worst , It was time to lit the candle, my mother lit the lighter holding the burning lighter in one hand and my 3 years old sister into another hand , this made my special day into the most terrible day ever, she was about to light the candles when my sister with her tiny legs pushed my mother arm , the lighter slipped from her hand and on the cloth table ,it caught fire my dad grabbed me and pushed me towards the door he tried to manage the panic but it turned out horrible, a small child bumped into the table , the table fell, the carpet caught fire and then the curtains and then the whole house , everyone was running after their lives, I was literally standing trying to understand what is happening,this literally happened because of carelessness but then I noticed something I was moving own my own ……..no I wasn’t moving on my own the house was moving !! I looked everywhere for any sign of my parents , were they out? Should I leave but what if they would be inside and I left them , then I heard my sister crying my younger sister ,I followed the screaming and then managed to find her but to my horror I wished I wouldn’t have gone there or like… My mother was under the broken wall and my sister was sitting beside her , her leg under the broken wall. I couldn’t find anyone , what should I do?? The only thing I was thinking about, I picked my sister to look around, grabbed the fallen necklace of my mother and ran towards the door , most of the people were out now, some people dead and some burning , I ran but the door was blocked with fire. I looked for the window . I pushed open the window and stood on the ceiling looking out and then 1 2 3 go !! I jumped out and fell on the hard ground with my sister on my top, I got up, picked her up and then ran far from the house, not knowing where is my dad or my brother ,dead or alive and then my feet stopped and turned around  to get the last glimpse of my house and then slowly my house turned into ashes with the screaming of people from inside . I sat there unless looking how helpless I was, my aunt placed her hand on my shoulder “ Come on ,let me drop you both at the foster care” she said ,I nodded , I knew it,this would happen , who will keep 2 restless children so I got up and looked at the necklace of my mother I saw my mother smiling at me and saying “ she is your responsibility” pointing at my sister who was beside me looking at our burnt house. I looked at my sister and sighed , tears sliding on my cheeks, my aunt grabbed the necklace from my hand and said “ Give it to me , It will be of some use” this was it , offcorss it would happen , I have read this all in books before but never even thought of that it will happen with me but I was ready.

3 years , we spent in foster care , me and my sister , wanting the love of parents desperately. After 3 years , on 3rd of October,there came an old couple wanting to adopt 2 children to finish their loneliness and luckily we were chosen. We lived years together, groomed ourselves , learned everything that a parent teaches their children . Everything was going perfect but I think odds are never in my favour, both of my step parents died and we were once again left alone, I had already graduated and my sister was going to be in a month or so . Well there was a lot of money that they left and it go for 5 years if we used them with care but my little sister changed her behaviour , going out to parties , coming back at late night and if I asked her anything she would rudely tell me that not to come in her way, soon there was a need for a job so I went for it , I did a job and earned well, I gave my sister money every time she wanted, I didn’t wanted to say her no she was the only one I had, because of my business work I had to go for a trip to london for 2 years, I was relieved that my sister had graduated so I told her to start job and she did even agreed. The day I was about to leave she asked for a heavy amount of money to start her business so I did give her . After a month or so I got call from my sister that she is tight in business and she has sold everything she has and she still has to pay all the loans she had taken to start her business because the money I gave her weren’t enough, I was shocked that whole month she hasn’t called or even received my calls and now she has called just for money?

Well I sent her a larger amount this time and called her back ,thinking she would be happy but she didn't receive it . Well after a month again I got a call asking for more money as the previous weren’t enough , I was surprised as the loan amount she has told me could be easily given by the amount I sent her , well this time before giving her money I checked her businesses on internet , I didn’t find anything , I checked her instagram and then I found where all those money where going , my sister was in a expensive store buying several clothes and uploading pictures , I shut that down and decided to send no more money, I received a abusing call from her but then it was the last thing , I changed my number , I was in a shock that my only family member, the one I love the most could have done this to me but now  I knew I was doing the right thing

Why does this happens that in-life there is happiness for a little time and sadness,

sadness forever?