See, i thrive off that a bit... i always stress over having the right map for everything i want to do, but i have come to realize that my players can be just as engaged when they use their imaginations. That, and i use the rule of three: Have three places preared, have three lore things prepared, and three encounters prepared.
We are a mixed online/in person group, using Foundry, so it took a bit to get the vibe right.
I also am doing an partial home brew Faerun, where Faerun gives me the overall structure, which takes a bit off my plate.
That and.. ahem.. borrowing... from all the fantasy novels and bringing them in as homebrew.
Gave my paladin a Sword of Truth, but the whole "you can only kill people you think are evil" is a curse mechanic of the sword. Also, he gets itchy whenever anyone around him lies.
The players found a magic bell that has charges which can be used for multiple 1st level healing words, or one mass healing word once per day, with 1d4 charges recovered per long rest.
I am lifting a concept of Holds-based magic straight from the Ericcson Esslemont GURPS rules (in my 5e Faerun, Mystra is Basically K'rul, and the weave is basically the warrens, but there is a deeper, more potent, far more chaotic form of magic that is dangerous).
My wife wanted to be a druid/harry potter character, so i found a home brew ruleset for her on potion making that expands her ability to brew potions and stuff, with the main limiting resource being time.
One of my players wanted to be Kalashtar, so i have a thing where her granparents fled with other Kalashtar to Faerun, and the Quori basically hunting her family down (yay for big bads!).
I also have another person who wanted to be from critical role's Tal'Dorei, so why not have a multiverse sized campaign where something his character does causes one of the villains and him to be pulled through to a new realm? Boom. Theres the story. BBEEG#1 was trying to do something. Player from Tal'Dorei is a powerful wizard thats expirimenting with crazy magic. Both do a thing, pull each other through to a new place for both of them. Quori want to be able to conquer places physically? Boom - whatever the player and BBEG#1 did weakened the barriers between universes. The Qouri discovered this and now they want to conquer every material realm on the multiverse. Kalashtar character doesn't realizes shes the lineage of the long-thought- dwad taratai. Qouri inspired recently found ways to navigate the multiverse, and murdered most of her family. Boom BBeg #2: qouri invasion.
For sandboxing, i am trying to run with three possible BBEGs, and reacting to their choices.
I made a little solo game outside that i used to determine the BBEGs' actions to some extent and to take some of the pressure off of me having to actually make decisions.
Plus... playing it out, super fun, i can change it if i want to, AND i can throw in flavored encounters to slightly steer the players focus...
I also try not to get attached to NPCs.
I LOVE creating them - whenever i play video game RPGs i spend way too much time in character creation, and then end up restsrting five pr six times before gettig my "playthrough" character...
So i have well over 150 NPCs in Obsidian. All mostly detailed out and such.
And that doesn't include the ones msde up on the spot because my players want to go ask a random guard where the cheapest booze is.
But i will be carrying them from campaig to campaign, so its not wasted work :)
But, for some reason, many then choose denouvo instead...