Never trust an abstract principle by itself. Come up with your own concrete examples.

Tinker with these examples to improve your understanding of underlying factors of the principle.

Look for examples that might contradict the principle and understand why.

Let us take DRY for example:

If I make a change in one place, and I have to know about 4 other far away places to make the same change, will that cause problems?

What if there two duplicate lines of code in the same file, right below each other?

What if it's a 3000 line file that's duplicated? How about a 4 line function?

What if changing it in one place doesn't mean you have to change the other place?