The first half of the sentence is saying, "Don't do things the hard way (hacking) when you can do them the easy way (social engineering)". The second half is saying "Everyone should know this."

"It's not clever to hack [with social engineering] something that you can socially engineer"

vs

"It's not clever to hack something [i.e. with technical exploits] that you can socially engineer""

Interesting. I am not a native speaker and I cannot make sense of the op's sentence in a way you understand it. How did you understand op's sentence in the first place?