Budget is one of the most essential parts of every project, so that you had enough money for every stage of it. That's why you need to plan the amount of expenses thoroughly.
Actually, budget is the total amount of money you'll need to finish the project successfully, but the vast majority have no idea how carefully it needs to be organized. Here are some points that have to be included in your budget:
Salaries of workers, including taxes
Studies or data to support your idea
Consultants, market research, legal advice
Another reason why being able to arrange the budget is so important are investors. Experienced and trustworthy investors are always to notice every single detail so if your budget isn't planned correctly, they might reject your offer to cooperate.
On the other hand, even if investors haven't noticed a mistake and the capital you mentioned isn't big enough to fulfill all your goals, you can get into trouble.
One of the biggest myths is that social projects (like raising awareness about some issue) doesn't need any money to be invested, but actually they still do! Venue, speakers, food and drinks have to be provided and these resources aren't free!
Summarizing everything above, budget is a serious topic to work with, so take your time, consult professionals and don't be afraid to ask for help, because this is one of the most important and complicated tasks you'll deal with on your way to creating a successful company!