This article, the title of which I won't transcribe here because it has a swear in it, contains some truly excellent advice on how to make things difficult for your characters, and, hence, exciting for your readers.
I am one of those writers who hate to make things truly awful for their characters. I don't like to make anyone suffer, even if they're fictional. But I have to admit, a main character who doesn't suffer makes a story bland. Conversely, a main character who finds strength, power, and virtue through adversity makes a story fulfilling. At least as far as I'm concerned. And even anti-heroes, for whom the virtue is optional, do better with something to struggle against.
Oh, and as you can probably guess from the euphemistic way I'm handling the title, the whole article is pretty full of swears. Read at your own risk.