Creator of Mario Brothers and the Wii gaming console Nintendo started off in 1889 selling playing cards. They proceeded to dabble in taxis, hotels and food. They won some and lost some, but using the profits they accumulated over time they entered the video gaming arena in 1976, where they continue to be a dominant player.
Samsung was founded in 1938 by Lee Byung-chul. He admittedly received an inheritance, but the first thing he opened was an unsuccessful rice mill - hardly the Samsung we know today. He then tried his hand at trucking. Today Samsung make ships, consumer electronics and continue to sell insurance.
You may have intentions to build a Samsung, Nintendo or SpaceX type of company, but these types of operations require a large capital outlay. Don't be afraid to commence with something more practical initially in the interests of generating the cash you need. Technologically advanced sectors are more lucrative but they also carry heavier risks that only capital (and a strong stomach) can absorb. When debt finance and venture capital are hard to raise (a problem thousands of entrepreneurs have), you have to fund expansion and new ventures from your current profits. Nintendo failed at taxi services and love hotels, but the capital they accumulated prior to that from selling simple products allowed them to continue to take risks.
First, be practical, then become more idealistic and imaginative when your bank account warrants it. Many of the basic lessons you learn early on from running a simple business will be just as applicable to one that makes rockets. You have the option of evolving and growing into the business you want to have - it doesn't have to be done in one step. There's no need to give up on your dream; you may just need to take a few interim steps before you can launch it.
The Happy Uprising is available on Kindle for $2.99 (prices may vary by region).
Amazon Review: "This is a well written, smart and happy book about getting oneself out of the ruts we often find ourselves in - not only in the job market but also in life. Highly recommended - well worth the price."