People generally associate important decisions with difficulty. Consequently, if a decision feels unexpectedly difficult, due to even incidental reasons, people may draw the reverse inference that it is also important, and consequently increase the amount of time and effort they expend. Ironically, this process is particularly likely for decisions that initially seemed unimportant because people expect them to be easier.
I know very little about psychological experiments, so I’ve no idea if their experimental design is good or not. All I know is that I find myself doing this all the time: I compartmentalize decisions, breaking them down into parts. I feel like I have to look at all the parts/issues before making the decision…even if the decision is what brand of toothpaste to buy. Luckily, I’m learning to slap myself out of it.