Nameless

I dont know how much this makes sense to you guys but why dont u mix the dino oil with synthetic? I've been doing it to all my other cars except my FD (all dino oil), and all my cars have been living (or lived) a healthy life while under my care). I dont know why I started doing this, my neighbor was doing it, and he taught me how to change oil back when I was 16, and I've been doing it since.

Is there any problem with doing this...to any car, let alone an FD?