Dark Souls has never exactly been an uplifting game. Extraordinary, yes; cathartic, frequently; cheerful, not so much. Despite the fact that Dark Souls is probably my favourite game of all time (I even wrote a book about it), sometimes playing it can get me down, especially on those days where no progress appears to be forthcoming and even normal-sized enemies are ruining me. I've been having a great time in Dark Souls 3 so far, but the area I'm at right now is BRUTAL.
Everybody has off-days with Dark Souls. But there are always ways around it. Whether you've hit a wall 30 hours into Dark Souls 3 or you're new to the series and having a bit of trouble settling in, if you're feeling discouraged, all you need to do is avail yourself of Dark Souls' amazing community and you'll soon be back on your way.
Spend some time helping other people out
Dark Souls has always had a smart online play system where you can invite other players into your game to help out. But doing so also opens you up to invasion by other players, so it's a double-edged sword. It's also an absolutely crucial part of Dark Souls. Since the first entry, I've refused to review these games before release, because the community and online play is 50% of the point of Dark Souls for me. You're not supposed to get through alone. Some people insist on playing the entire thing by themselves, but those people are missing out.
Perhaps you don't want to spoil the challenge for yourself by getting people in to help with bosses. That's totally fine. But it's not all about asking people to help in your game. There is a TREMENDOUS amount to be gained from helping others out in theirs.
If you're having trouble getting to grips with a new area, place your White Sign Soapstone summon sign down on the ground (you can get the soapstone from the vendor lady in Firelink Shrine, if you don't have it) and allow yourself to be summoned. Not only will you get to explore the new area with a fun stranger, who may or may not know more than you do, you don't even risk losing any souls if you die.
Last night, in an area about ten hours into the game, I spent a full 40 minutes absolutely rinsing the place as a phantom with a stranger in need. We defeated three separate invaders, felt our way to two new bonfires, killed almost everything in the area, and accidentally found a boss. It was great. Naturally this progress wasn't replicated in my own game, but when I appeared back in my own world, I knew what awaited me.
I also went home with 14,000 souls, even though I'd died in the middle of the boss fight. Here's the thing: there is no reason ever to have to grind in Dark Souls. If you need souls to buff your character up or buy some new stuff, why would you spend boring hours killing the same enemies on your own when you could be helping other people defeat bosses and come back with more? Having someone else around adds a bit of levity to the game, too.
If you'd rather explore new areas on your own, you can always put your summon sign down in an area you've already completed and help someone else get through and defeat the boss. You will be someone's hero. It will give you such a warm and fuzzy feeling, and imbue you with renewed confidence to forge ahead in your own game.
Try out a new weapon
It's easy to play conservatively in Dark Souls, and fail to challenge yourself. I suffer from this. When I'm somewhere new, or fighting a new boss, my nerves get to me and I end up defaulting to a big shield and a one-handed sword in my right hand, instead of playing like the lightly-armoured double-dagger-weilding thief I really want to be. There's nothing wrong that playstyle, but there's so much fun to be had experimenting with double scimitars, and whips, and halberds, and magic, and the tens of other unique weapons and skills on offer. Especially now that every weapon in Dark Souls 3 has a new weapon skill, which greatly expands what you can do with it.
If you're butting your head up against Dark Souls 3, switch to a completely new weapon and head back to an area you know well. Then try killing things in a new way. It can help to rejuvenate the game, and get your confidence back up.
This is another good reason to make yourself available to be summoned in other people's games: you can try out a new weapon and it doesn't matter so much if you die. (Well, your summoner might get a bit annoyed).
Ask a friend - or a wiki
It's wise to be careful with the Dark Souls wikis. They contain treasure troves of helpful information, yes, the product of thousands of players' collective experience, but it's easy to accidentally come across a page that will ever so slightly ruin something for you. If you've hit a wall, wikis are a good place to turn to for help; you can also read about areas you've already visited, and see if someone's discovered something that you missed. But a better solution, especially if you're spoiler wary, is to ask a friend.
Dark Souls is immeasurably more fun when experienced with friends, whether they are actually in your game or not. I fondly remember the long email threads where other early Dark Souls players and I swapped discoveries, tips and motivational GIFs. Right now I'm playing Dark Souls 3 alongside my partner. If you don't know anybody IRL who's going through Dark Souls 3, people on the Reddit and even on Twitter are generally extremely helpful. I've even heard of people who've formed enduring friendships through Dark Souls support groups. It's a game that brings people together and creates shared stories, which for me is the most extraordinary thing about it.