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I disagree, it takes lots of time but it is possible. Personal example: I have an electronics engineering degree that was 1 semester short of a physics degree, so I learned quantum mechanics, electromagnetic field theory, transistors, and how to create a CPU (I even created a CPU out of simple gates and way too much wire wrapping). I love computer software, so I learned assembly, how to write compilers and operating…
Jack of all trades, master of none. I don't think it's bad at all: at least you can specialise at something (quicker) whenever the need arises.
I guess my key point is that you always need to keep learning, and don't box yourself in too much. Ideas from elsewhere will show up... being aware of them makes it easier to use them and be ready for them.