Some people feel railroaded if you start your campaign with one of the best starter vignettes ever:
DM: You are naked in a dungeon, find your way out ....
Then your modern players, not used to such scenarios: where is my starting gear / spell book / holy symbol thieves tools.
DM (raising his eyebrows): Well your captors have stripped you of your belongings.
Players: But wait, didn't we fight back, we did not even roll for that combat, we could have fled, escaped etc. You are railroading us into that situation.
DM (slightly enervated) : Well ok, so you got your starting gear and sitting in a tavern, roll for initiative, because some heavily armed guys enter to take you in. They are accompanied by some casters.
(After the fight) DM: You are naked in a dungeon, at - HP. make your deathsaves, everyone who survives can try to find a way out.
Player A does not make it.
DM: ok roll up a new char, you others wait a bit and get the benefit of a short rest.
Player A has finished his new char.
DM: Ok you other guys hear a cell door opening somebody is tossed into the room. Player A erase all your belongings from your sheet, the captors have held you in the streets and stripped you of your belongings. What? Did I hear railroad? You want to roll for that encounter?
Nah seriously, railroading is a bit different than that. Railroading is to have every minor goal resolved as per script, one way or another. But even the best campaign has its key milestones. A good DM tries to hide and camouflage them as best as he can if he has to wing it, so these are met. Very good adventures make it by design, that PCs will almost certainly decide to meet these milestones themselves without feeling railroaded.