What is the best way to determine all of your needs?

First you are talking about needs that you have to transform into requirements to create the product. Second, you have two type of requirements: product requirements and project requirements. From product requirements you will create project requirements. Third, to elicit needs you have quit different strategies. One of them, if you do not have posibilities to elicit from stakeholders then create a first version with features you elicit from other sources and put it to work to get more needs and information from users. That is the strategy that some organizations like Google has followed with products like google mail.

I fully agree with Sergio - He nailed it.

It is all about Product requirements and from which you will determine the project requirements.

I need to say that Sergio made an excellent description.

If you can validate with stakeholder or users before the first version that would be a plus.

Crystal, the point here is: could I get needs about the product I will create or not? I prefer to say system because sometimes to focus on product you could lost that it will be part of a whole system and then you fail to create the right product. So, the technique does not matter. What matters is the posibility to interact or not with the environment to get the needs. That is because I prefer to talk about system. After that you can search the technique. Forget about the technique in the first time and focus on the enviroment where your product will perform. For example, you can use this as a guide: http://www.projectmanagement.com/blog-post...-right-solution
But before that, you have to understand the external environment (you can use PESTLE analysis as a tool) and your internal environement (the article could help). You do not need to loose lot of time. But you have to have and idea about that.

Sergio,
Thanks. I'm glad you came back with this comment. While in my planning session, this exact question came to mind. Thanks again for all that you do.