One aspect of game design that many people point to when wailing about the lack of difficulty in many games these days is the save system. Older games, they argue, doled out saves like precious gems, and thus made the whole experience much more challenging. 'Where's the difficulty when you can save wherever and whenever you want?' However, as designer David Sirlin argues in a Gamasutra article, this is a false dichotomy: "We can allow the player to stop playing without excessive penalty and make a challenging game. It's just a matter of defining what 'saving' actually means." In short, there are plenty of examples of challenging games that don't punish the player for having other things going on in their life that don't allow for structuring a day around gaming:

A save system should allow the player to stop playing at any time, allow the player to pick up where he or she left off with as close to zero replaying as possible, and save as automatically and seamlessly as possible, so the player will not forget to do it.

Saving should be treated as one of the player's natural rights, not an earned privilege or a game mechanic around which to make strategic decisions.

The design space we have to create new games is so unthinkably large that we lose virtually nothing by restricting ourselves to designs with friendly save game systems that don't presume to override the real-life needs of players.

I usually wind up gaming on the fly — a little bit here, a little bit there — and the inability to save 'meaningful' progress quickly is one of those things that irks me. I sometimes resort to leaving my console on, wondering the whole time I'm out of the house if the damn thing is going to overheat and my house, possessions, and dog are going to go up in flames; I don't really need to be punished because I can't schedule my day around gaming. It's an interesting article and rebuttal to some of the 'difficulty discussions' that have been going on lately — Sirlin pretty successfully argues his point that making save systems that don't punish the player for having to put the game down aren't (necessarily) to blame for the lack of difficulty people are grousing about.

Saving the Day: Save Systems in Games [Gamasutra]