Why Google ranking is so much fluctuate?

[webdeveloper]

The main reason behind fluctuation in Google ranking is only that they are updating their algorithm. As we all know that Google is a search engine and on search engine we always search some contents so Google is changing its after a time period for make it secure from spammer and bad links which can affects the website. So, sometimes updates are in our favour and sometimes updates are in not favour. So we face fluctuation in ranking.