Is business plan necessary for business to succeed? if yes so why ? and do you believe in have the steps in your mind instead of papers ?

If a company doesn't have a specific plan then, for me, isn't a company but a joke. You can't expect to bring positive results without any arrangements before you start. Success isn't going to drop from the sky! Every job needs a vision and the ways to achieve it. So every entrepreuner must have an idea and a programme in order to reach his/her target. And it's better for me to be written down and from time to time review and check them. 

According to me, yes a business plan necessary for business to succeed.

If you are starting a business first you know which will be your customer base, for ex. adults, children, teens, domestic use, corporates, etc. Then according to this you need to make ads or marketing.

Then we should also take in account all the risk factors like initial loss, less customer response, etc. and plan on how to tackle these calculated risks.

Unable to understand your last question.

An approved business plan is necessary for business success mainly because it clearly communicates what needs to be done by whome and when. It also facilitates assissing effects of any deviations on all participants and deciding how to effecctively handle such incedents. I would rather have the business plan written and approved. This might be spared for small plans handled by one person.