An experienced designer can defend their decisions confidently. The key to being able to defend your decisions is to know why you made them, and why they make sense.
I've written an article about 10 psychology concepts that can be translated into design.
If you'd like to read the article, you can do that here:
https://medium.com/@onepixelout/10-psychology-concepts-for-designers-1c680a12f8d8 (and also on my own site, www.onepixelout.com)
I'd really appreciate feedback on the illustrations, I'm still quite new to this.