Re: How gentle should a DM be?
To clarify, or perhaps expound on what I said earlier...
I've been in groups where the party got itself into situations that had even the GM shaking his head and asking how everyone was going to get out. And they not only got out, they practically walked away, completely unscathed, because they came up with some really bizarre and outrageous ideas that the GM looked at and said, "Y'know...I can't see any legitimate reason why that WOULDN'T work...so, yeah, roll the dice and let's see where it goes." And the dice were very favorable.
I was in a Star Wars game with a woman whose character seemingly couldn't shoot her way out of a cardboard box...I've never seen anyone so consistently miss dice rolls to attack. But only until her character was stunned, or wounded, and had a dice penalty. Where she couldn't hit anything with all of her dice, once she had a penalty, she could shoot the wings off a fly at fifty yards.
I've been in groups where the GM had carefully set up an encounter that was supposed to be an extended battle that would last for hours...and one person, using one magical item in a way the GM had never anticipated, ended it before the first attack rolls ever got made.
I've also been in groups where nobody ever seemed to be able to get anything to work properly. The dice didn't like us, or the skills people had taken just didn't mesh well with the situations we found ourselves in, or we were just far enough out of sync with each other that every time someone got the bad guy on the ropes, nobody had a follow-up ready and he had time to recover. I played in a D&D group where everyone seemed to have something useful to do except my assassin, who had absolutely nothing that was useful against the giant animated raven statue he ended up tangling with...the only thing he could do was take a tumbling dodge to try and stay behind the stupid thing and hope literally ANYONE else in the group finished with their bad guy and could come rescue him. And he made an incredible showing for himself...I think he dodged the stupid thing for seven consecutive turns before the dice failed him...and he took a beak right through the chest that killed him.
I was very briefly in a Firefly game on here...briefly, because the GM brought my character into the game just in time to be arrested on suspicion of mutiny. He was the only one on the ship, had no idea what happened to the crew (had no idea who the crew was, even), and no matter how the situation was explained, the officer that arrested him was determined that he'd done it. So, three days after my character joined the game (two of which were over the weekend, when I was working fourteen-hour days and didn't have any time to be online, much less posting at length in a game), he was executed.
I've had a pretty broad array of levels of gentility from my GMs...
How gentle should you be? Well, that depends on the group. The DM for my assassin was incredibly gentle and actually repeatedly fudged the dice rolls to give the rest of the group time to heal my assassin enough that he wouldn't die. The GM of the aforementioned one-item-takedown of the bad guys was set up to be incredibly cut-throat...this was supposed to be a battle that would push everyone to their very limits and might actually kill a couple of characters, he told us afterwards. But the group was ready for that kind of action. I'm still trying to figure out what the GM of the Firefly game had in mind, and that was close to a decade ago...
You have to exercise your best judgment, based on the players and the situation in which they find their characters. And there's a broad range of options between one-legged kobolds and ancient dragons...don't get sucked into the trap of thinking it's gotta be one way or the other.
As mentioned, there is no good one-size-fits-all approach to it. And, yes, you may misread your players and make things too difficult and they quit. You may only make things LOOK too difficult and they lose their nerve. Or you may get things too easy and they get bored. But life doesn't just give you super-easy vs. mega-difficult options...not every encounter the group has needs to be ratcheted up to one step harder than the one before. There's something gratifying about occasionally facing off against a horde of orc raiders and coming out of the encounter looking like the Angel of Death just had a field day with your help...there's also something satisfying about facing a problem that you weren't sure you could handle and getting through it. Sometimes, you need to be gentle. Sometimes, your players aren't at their best, and while I don't think you should ever coddle a player unless they're involved in their earliest role-playing experiences, if you sense that the players are a step or two off their stride, you'd be well-served by dialing back the lethality of the challenges they face until they find their legs again. But there's not a clear formula for when to do it, or how much to do it, or whom to do it for, etc. That depends on you, the players, the game, and the immediate situation.