One of the best ways to explain what the fatigue issues with lupus is like is with the "Spoon Story" on butyoudontlooksick.com but I've recently realised another way to explain it, that might make more sense to some people.
Everyone has a certain amount of energy for each day. Someone with lupus generally has a bit less than most other people do. The energy we do have, we have to budget, in the same way as we have to budget our money.
We have to decide what in the day is worth spending energy on, and where we can save a bit, so we've got it when we need it. It's possible to keep a little bit in reserve at the end of the day, so as to start the next day with just that little bit extra.
With your money, if you decide to set an amount aside for eating out, you could use it in little bits and have lots of trips to a fast food place, or you could save it all for one special outing to a high-class restaurant. It's the same with energy, you could spend it in little bits here and there, or save for something special.
It's also possible to push past the limit, to put just a little bit on the credit card. Like money, the energy credit card comes at a cost - suddenly the day comes when you have to pay it all back with interest. That's not pretty. Eventually, if you're broke, you're broke. With money that's a problem. With energy, it's also a problem. For a lupus patient, being "broke" in terms of energy, can mean several days of not being able to get out of bed, of functioning at only the most basic of levels.
With careful budgeting, someone with lupus can do anything anyone else can do: we just can't do everything everyone else can do.