u/Gettor

Explanation ("Hindering their LR" was used as a massive oversimplification):
We had a game with kobold lair and young red dragon as their boss, pretty standard DnD dungeon. Lots of traps and ambushes from kobolds, players had lots of fun chasing little buggers through the tunnels. Equally lots of fun when someone fell into kobolds' trap, other PCs helped them out while laughing about how clumsy they are, 10/10 so far.

Then came the cleric stating they're out of spell slots, so no more healing. Players also checked that they're short on HD's, so short rests are no longer beneficial. They decided to fall back, return to tavern (half a day worth of travel) and return tomorrow.

Lo and behold: the next day dragon boss called in reinforcements, some bugbear muscle, kobolds rebuilt and improved the traps.
Players acted like they've been betrayed: you know things look dire when they try to tackle the problem by stating that you (as DM) are unfair instead of trying to address the problem in-game.

So we talked - about how it makes sense in-game, but also how it makes them feel like their progress was meaningless and 'how do they know I won't pull something like that again'. I was shocked - 'again'? They made it sound like monsters regrouping and reinforcing their lair during the night was entirely my fault and I shouldn't do that again.

It spiraled out of control from there - I might have used the phrases "you don't get plot armor" and "actions have consequences". They argued I should've told them beforehand that this could happen. I agreed and promised to be more upfront about consequences for PCs that have high enough passive Insight and/or Investigation.

It seemed fine... for two sessions. It soon became obvious that the enthusiasm of my players had died  - they were reluctant to do anything in the game in fear of consequences and because they genuinely felt I robbed them of that victory (meaning: progress in the dungeon). We wrapped up the campaign and decided to spend our game nights on board games instead.