Everything should be made as simple as possible, but not simpler.
The Most important thing , I've learned here is to simplify stuff as much as you can "understand" every single detail of it . That's it , no more ....
My conclusion is so close to what Albert Einstein has told before !! But I didn't understand it till I figured out a concept in "Reinforcement Learning" during "Machine Learning" course . I'm used to give up or neglect very tricky and hard problems before , but for the first time in my life (yes,it's sad) , I decided to change my mind.
And guess what ?? By only spending one hour on one page , the result was awesome and I did understand the whole chapter afterwards .
The moral result : NOTHING is hard ; Some stuff just need more focus and dedication ...
That's it friends :)