1) Building a startup is risky
Learning new marketable skills is not risky. Building a company will teach you many things that are highly valuable in the job market. It won't be easy, but you can overcome any issue if you are eager to learn.
2) You need investments
Time can replace money. You can build a tech startup for 2$ a month (price of a domain name) and learn all the necessary skills on the road.
3) Starting a startup is hard
A startup doesn't have to make money right from the start. You don't even need a product. You certainly don't need to register a business. What you need first is market validation, and that doesn't take any money if you do it well.
4) You need a business plan to create a startup
Hell no. Business plans are for investors. You need one yet. By the way, if colleges could stop making the students write business plans picturing imaginary startups, that would be nice.
5) You can live off passive income with a tech startup
Absolutely not. Startups are temporary structures meant to evolve by definition. This constant reinvention takes a lot of work.
6) You need an accountant
Are you making money out of your product? If not, you don't need an accountant.
7) You need a lawyer
8) You need to know how to code
No. In most cases, you can build minimum viable products using free online services.
9) You need to study startups before creating a startup
Building a startup is a war. You won't know what it's like from books. You have to go on the battlefield to confront yourself to reality. The beautiful thing about startups is that there is no guide book for success because it's about acquiring tacit knowledge relevant to your domain expertise.
10) Building a startup will make you rich
You can make a lot of money and still be poor. Wealth is both a mindset and a set of financial skills.
11) You need co-founders
You don't need co-founders when you are starting.
12) You have to be careful when you share your ideas
Ideas are worthless. Everybody copy each other because that's how we learn, but it doesn't mean people will go out of their way just to steal your idea. It ain't so special. Your ability to make this idea a reality is what matters (the skill known as execution).
13) I have to give up on my project because X is already doing the same product
No. Be confident you can bring something others can't. Innovation is not invention. Innovation is built upon existing concepts.
14) Your product has to be perfect before launching
Launch as soon as you have something functional. Launching means putting your product out there for users to see and try. It doesn't have to be a huge launch, but you need feedback/validation asap.
15) I have to leave my job to build a startup
It's better if you validate your idea with cold hard cash before thinking of quitting your job.