Hiya!
I run a believable, logical and consistent campaign.
What I mean by that is I don't "design adventures/encounters" around the PC's. I design them around the world. The PC's are the ones
"interacting with the world"...
not the "
world interacting with the PC's". (I hope that makes sense).
I have played in a few campaigns over the decades where the DM "designed" the adventures, NPC's, and basically the world, around our PC's. Every single one of those 'campaigns' felt like a self-contained group birthday party. Every PC was "special" and "destined for greatness". It didn't matter what we did in-game...the pre-defined activities were already laid out in the schedule. There wasn't any sense that our PC's lives and destiny was in our own hands. At the end of these campaigns (always fading out after a few months), they felt like "stories we were playing a part in". Like we were spectators and not writers.
Anyway...by switching up to a "campaign world FIRST...player characters SECOND" mentality I give my players the indisputable fact that they are the ones driving. I learned this after about a year or two of DM'ing (back in...oh, 1981 or so). I've been DM'ing this way ever since...and I'm almost always DM, so I must be doing something right.
So, if you don't want your player characters to go from "zero's, to heroes", don't set your world up to foster that. Let the PC's decide their own fate. Sometimes they will choose things far beneath their capabilities, and sometimes far over them. Just last night, for example, our new campaign (as in 1st real session for this one) had the PC's making their way to "The Cave of The Tenticles". A supposed sea-side cave guarded by poisonous and rather agressive octopi. So dangerous that the pirates around the area have stopped going there to hide treasure...or return for it. The PC's find the cave and hit the beach. They are attacked by Sandlings (old 1e monster originally created for A4, In the Dungeons of the Slave Lords...I used the 5th Edition Foes MM by Necromancer Games). They are CR1, but there were 8. The group of 5 PC's almost died in three rounds! They decided to hot-foot it out of there. Nope. No way are they going to do that, they figured. So...back at town, they took another job; kill an ornery badger who's been pestering a farmers cows. Success! One dead badger, and 2gp reward.
The point of all that is: The world has stuff going on. The players make the decisions on what to do. If you, as DM, are "designing encounters" based on your PC's capabilities all the time, you are going to get the "barely able to kill goblins one day, then killing off gods by the end of the month" because that is what
you are designing. It doesn't matter, from a player perspective, what they 'choose' for their PC's because you, as DM, are designing encounters around their PC's and not their PC's
choices. For example, if they are all 3rd level and hear of a white dragon in a nearby ice-cave and head off to get it and take it's treasure...you, as DM, should
not be designing it so that they have a "reasonable chance of success, as 3rd level characters". You should be looking at your campaign world notes, seeing that this white dragon has been called "Frostbite" by the locals for the last one-hundred years, and that it is feared and avoided by all. You pick an Adult Dragon, design it's lair based on what it would logically be for such a beast, and let the PC's walk in to their deaths...or, if they're smart, walk up to the area, realize the folly of what they are thinking, and turn around, beating a hasty retreat before even getting close to the cave entrance. By doing it this way, there is not expectation of "fairness from the world". There is not expectation that "we're 1st level, so we fight goblins", or that "we're 20th level, so we fight demigods". There is no "expectation" of anything other than what the world tells them to expect. "The goblin caves...probably has goblins in it" is the expectation...not "The goblin caves...probably has goblins...lead by a trio of mind-flayers, their ogre henchmen, and a contingent of mid-level drow...because, you know, we're all 8th level".
Sorry for the length!
^_^
Paul L. Ming