"As you cross the woods, there is a fork in your path. For the sake of transparency, I'll let you know that if you go to the left, you will encounter an Ogre Mage who you must defeat in combat. The mage has 37 hp and can cast magic missle 3x/day. To the right is something that that I haven't prepared, but I'll
figure something out frame the scene with respect to the players' choices (to go left or right). Probably combat, if you want. In either case, if you successfully complete the encounter, tbd, you will face another fork in the road. In fact you will keep facing forks in the road until you successfully complete 3 encounters, after which you will reach the town, which you will recall was your player-authored goal."
Problem solved!
I kid, I kid...in reality I think some degree of these things are good dm practices in any edition. Situations and conflicts are more meaningful when the stakes are at least somewhat known. The world
should react to the PCs actions, which then help determine the "plot" rather than pre-imposing it. And I think transparency about what you have not prepared + randomness (via dice and encounter tables, for example) is more fun for everyone than heavy prep + illusionism.