YOU actually have to do all the planning.
You can’t fall back on your travel buddy who’s far better than you are at deciphering train and bus timetables, even when you speak the language they’re printed in and he doesn’t.
You can’t divvy up researching the “cultural stuff vs. historical stuff” according to who’s more interested in what, to make it easier to determine what’s actually worth seeing given your time constraints.
You have to read both the “Hey stoners, want to see some cool shit?” and “Hey American middle-aged dentist traveling abroad, want to see some culture?” travel guides you’ve purchased instead of having one person read one and one person read the other, and being able to quickly figure out which sites are recommended by both.
You can’t fob stuff off on your travel buddy when you have a busy week and allow him to fob stuff off on you when he does in turn.
And you have only yourself to blame when you’re up until almost 3am a month before you leave, and you still have only a vague idea where you’re staying or what you’re seeing.
I’m sure the freedom to do whatever I feel like will come in handy when I’m actually bouncing around Spain, but I seriously underestimated how much more of a pain in the ass the planning process becomes when you’re doing it all yourself.