Ages ago one person or small group of friends could create successful completed project. It was possible because they could understand whole technical stack from hardware to UI, i.e.:
The clock is ticking, products becomes more complex. New entities & abstractions are appearing. They are needed for reducing complexity(OSI model, OOP, etc.. ), they goal is create domain area. It means that a person can concentrate and operate small area of knowledge without extra information.
As a result a project/product can’t be done by one person or small group. However there are a lot of different startups. On one hand they usually are created by small team, but on the other hand the small group creates only MVP; if it works, when team will grow, because a lot of engineers with a lot of specific knowledge will be needed to do stable product.
A glorious day is upon us. There are a lot of people who created projects from hardware to UI. However reality is that hard skills are becoming less important than soft skills. It is happening because if you are really good ingenier and rotten apple it will worth nothing, you will not be able to finish a project without team.