Good mechanical design reference for non-engineers?

I've gotten far enough along with Fusion 360 to know that I don't know what I'm doing when it comes to mechanical engineering. I've designed some cable supports for seasonal lighting that are working well, but I know the design has significant weaknesses, particularly at the bottom of the loop.

https://i.redd.it/mfyb34do2q421.png

I've seen that a double-loop at the bottom of carabiners is common, for example, but I'd like to understand why. I've gotten so far as doing a rudimentary simulation and confirmed that the 3D printed part does, indeed, break where indicated. I'm just looking for how to proceed next. I'm not expecting to be an expert, just gain some practical tips.

https://i.redd.it/seofu20l2q421.png

Somebody posted a link to http://507movements.com/ recently that has been very informative. I'm looking for a similar overview on strengthening mechanical parts I design. I'd appreciate any links to good sites or references on the topic.