Why do we dream?

Because of the data stored in our subconscious emerging during sleep and overtaking the conscious

Because we want to success in our life and without dream you never acheave your targate 

To Better Our Reality

And I don't need 25 characters as requested by the website. There. 

We dream only for the satisfaction of self esteem...

The most honest answer is that we do not yet know the function or functions ofdreaming. This ignorance should not be surprising because despite many theorieswe still do not fully understand the purpose of sleep, nor do we know the functions of REM (rapid eye movement) sleep, which is when most dreaming occurs.

I agree with Hatim. Just to add, the mind is free to associate events, people and places randomly during a dream which can result in both pleasant and scary scenarios. Consider dreaming as a way for the mind to process what you are feeling and thinking before you fall asleep and make its own links based on your desires, fears and social expectations/limitations. It has no filter...so it should never be used to dictate how you wish to proceed with your everyday life. Following through with a fear or desire that you have dreamt could lead to unpleasant results as the society we live in may not be accepting of the outcome. Being lead by a dream you had can also leave you with irrational fears and expectations. All this said...enjoy the dreams if they are pleasant and ignore the unpleasant ones. Follow your day dreams...they are ones that reflect your true and more achievable desires. Good luck!

The dream helps the individual to set his vision and the strategy to acheive it.

This hypothesis defines dreaming as a way to act out unconscious desires in a safe or “unreal” setting, presumably because to do so in reality would be unacceptable or even detrimental. But even in the 21st century we still are not sure why we dream. The only way to study dreams is to ask the dreamer.