I've been creating and redesigning games since I was young, initially with my younger brother who was crucial for gameplay testing. We started by combining simple games like the gambling ones to make something that had more strategy, complete with rules and whatever else we had in the house to add to it, those early years taught me about efficiency & making the most of everything.

Our first milestone was our expansion pack for Monopoly, using the space in the middle of the board to add a track, carefully measured to match the existing spaces etc. We placed the start of it on top of the income tax space :D from there there were additional properties including for existing colour sets (we made this before Mega Monopoly existed, and anyway that's a bigger board ours is an efficient use of existing space) and could then re-join the board from atleast one point in it. 

We also made our own Pokémon cards in Word and glued them onto cards we had too many of, the amount of balancing and testing was even more than our Monopoly expansion iirc. To this day I'm very good at it and Hearthstone, I come up with synergies that surprise even my brother. Gym Leader Challenge - the guy who showed me how it worked, I was beating him by the 2nd game, simply because I try any & everything to make efficient decks without using OP cards, which leads me to less-used cards and less-known combos.

In more recent years with sandbox games, I really got to implement my way of thinking, my desire to subvert what exists to make it deeper and maybe darker, so it can shock and surprise you the way secrets in games made me feel. I still remember my first Lego set, there was a treasure chest, that was hidden with leaves (one-piece plastic but with a hinge), the chest was inset into an alcove behind it under the hinge. May seem innocuous to write about but to my young mind this was life-changing. As for the secrets in games (Doom ofcourse), that I wrote an entire blog post about (the importance of atmosphere).