I believe Ravyne has it spot on.

I've seen so many people getting into the 'limbo' of creating the perfect (3d) engine, without actually finishing anything (no offense though).

Somewhere there's a dot on the horizon in the future, that's were you want to go.

Take that dot, go back step by step till where you are today. And simply take the next step :)

Whether that be creating your own engine for learning (if so, make a scope/ feature set, not limitless), or ship a completed game, or learn engine features a to j etc.

A good option is to do the dual way : working on a games using existing tech and working on an engine on spare time.

Once the engine is stable enough switch to it and update it based on the game features needed during the development.

Thanks everyone for now,

After I read all the replies and thought about the subject for a while,

I came to the conclusion that I want both things: and make a game and learn about how to make

an engine/what mechanics are behind a game(engine), so altough I never thought about it, the answer that Alundra gave

is very attractive.

I would make a game in Unreal Engine 4 in some moments and in others read Frank Luna's Directx 11 book

and after that start to make an engine and improve that.

Two questions:

1) Is this possible/reachable (i.e. don't you think I will completely lose track of eveything/confuse both things)?

2) Will learning about Directx/making an engine be good for my skills and experience in UE4 (for example: will I learn things

that I can apply and help me understand more, resulting in making a better game).

Thanks

Working on an existing engine will show you common design used and give you experience on scene graph.

Never forget we always learn from others.

Thanks,

I understand it works like that, but will it work the other way around as well?

For example: will learning about directx and making my own engine alongside making

a game with UE4 make me better at understanding UE4 and even make me a better game developer?

Game Programmer is a completely different view than Engine Programmer.

Generally, the two teams work in connection each other, if the game programmer miss of one feature the engine programmer implement it.

If you are alone, you should keeps concentrate on what your game needs.

UE4 is there to make you win monster time, it's a high level engine, that means you only concentrate on game development and not engine development.

Working on an existing engine will show you some design of development.