What's the difference between "difficult", "complicated" and "sophisticated"? It seems to me that "difficult" is a more general word to express the hard work involved in doing smth while two others have more specific meaning, but what exactly do they mean and how they differ?
A more general, generic, all-encompassing word to express the hard work involved in doing something. Something could be difficult if it required brute-force effort. Or, it required a lot of money. Or, a lot of courage. Any different type of difficulty.
This means a puzzle with many pieces, a math equation with a hundred variables. It is difficult in the particular way of being intellectually challenging through complexity.
"Complicated" does not always have to refer to difficulty though. It can simply be "composed of elaborately interconnected parts".
This word has multiple meanings. One of those is similar to complicated. However, you don't often say a problem is sophisticated, or a challenge is sophisticated. For those cases, you'd still use "complex".
Sophisticated is a term of praise: "this machine is very sophisticated". It embodies "complicated" and also "well designed" and "advanced".