This is about learning. Going through evolution of design from the ground up. Getting that joy that only comes when you do View Source and every single line is written by you.
Seconded, there should be a rule that says you must have tried to make everything included in bootstrap at least once yourself before your allowed to use it. Otherwise how will you learn?
That way when you do use it you'll have the knowledge to use it properly (and hopefully within moderation) well and you'll appreciate how much easier it makes life that much more!
I'd go so far as to say that after a certain level of experience, everyone should implement a compiler/interpreter. Automation is awesome, but it's better not to treat them as "magic".
This is about learning. Going through evolution of design from the ground up. Getting that joy that only comes when you do View Source and every single line is written by you.