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Your moving slow. Why ?
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He's moving slow because it's his project he wants to get everything done, Instead off rushing through and ending up missing some important stuff and have too go back and update/add it back.
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"Why reinvent the wheel ? When you could just improve the one already made." Metaphoric speaking.
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Why use a premade engine when you can use your own and be totally unique along with customization off everything and anything, Using a premade engine limits you to what exactly what you can do, Creating your own is pretty much better.
@AB; Good Luck, I hope this works out for ya ;D