It is certainly a truth that many people have a fear to cross the threshold of doing something for real. That fear is usually a fear of committing to a potentially substandard result or a fear of getting started on the meat of what feels like a herculean problem. In short it is the fear of failing.

As an university level educator that helps students with mostly technical projects (so stuff neither I nor them have ever done): This fear is very common. But what I dislike about this advice is that preparing the thing is often in fact a necessary step of (A) deciding whether the thing is feasible and worth doing and (B) a part of what is needed to do the thing. Drafting the general layout and data flow and UI for your software can save you hours later. Having a good and fleshed out concept for a game may tell you if it is even worth putting years of your own time into it, what resources you will need, a research essay on different ways to detect motion may e what makes or breaks the result of your interactive art installation etc.

So preparation is necessary, but true experience only comes from going beyond the preparation phase. Feel it is impossible to start? Usually that means there is something that you feel insecure with. E.g. your game might need an inventory system and while you have a great idea how it should look and work, you have no idea how to actually program it. And if that small part of your task looks impossible, it makes the whole task appear extra-impossible.

The best way to deal with this is usually tackling the problem head on and make it a proof of concept. The problem is you can't program that inventory, and there are many ways to go at that particular problem, but if you can get a draft inventory going that means your biggest worry is taken care of. That means dealing with the hard part first, even if you tell yourself it is just a proof of concept that won't land in the final thing is a good approach. Divide and conquer. The whole thing seems impossible? Break it down into smaller steps thst seem more managable.