Some desires lead to pain if unfulfilled, these are natural and necessary. Some lead to net pain and these are unnatural desires. Some lead to short-term pain in order to obtain net pleasure, these I think would be considered natural and unnecessary desires.
I agree with your premise, and
This last category would include something like "I'm going to go work out, which I hate, and which will bring me pain. But I'm doing it for the net pleasure of fitting into my old jeans or having a wild affair or going on a ski vacation &c."
…I just want to explicate what I think you're already saying: The desire is neither the working-out (event-in-process) nor the having-worked-out (event-concluded); these cause net pain. The desire is the wearing of old jeans, which causes pleasure. Only with this pleasure is the net pain needed to obtain it outweighed, confirming the classification of wearing the old jeans as a natural-but-unnecessary desire.
What surprises me – but what I would agree with! – is that if this same person was working out for the sake of working out, that would be an unnatural desire in that person (because, without the eventual wearing of old jeans, they don't get pleasure from the workout). (That's a useful detail to me, because before this conversation, my mind's examples for unnatural (limitless) desires were still centred around "vices" like addiction and power, and didn't readily contain "virtuous actions" like workout.)
I'll have to remember that for the next cold-call about gym memberships
Does everyone agree that "I desire to brush my teeth right now" is a perfectly acceptable ordinary English equivalent of "I choose to brush my teeth right now"?
The point is that we can use
desire = the object of desire
and we can also use
desire = choose
I cannot recall having encountered anyone who would, in their everyday ordinary speech, use "desire" to replace "want to" or "choose to". Do people say "I desire to take the trash out"?! To me, conflating "desire to" with "choose to”, “want to” or even "have to" either conjures up stilted speech in a tense situation or some sort of Victorian era dialogue.
Furthermore, for the sake of this discussion, the distinction is quite important to me, too: I never desire to brush my teeth; it's painful. What I desire is the sensation after having brushed them; that's pleasurable. That might, once again, seem like splitting hairs, but it makes all the difference between whether or not I end up doing it! Only when I call to mind and keep in mind how it is going to feel afterwards will I begin to move my mental cogs, shift where I am inside my mind, eventually move the body, get up, move towards the bathroom, and go through with it.
With repetition, this process gets easier: The ignition power required to spark it drops. Once it's begun, the various individual steps begin to fall into place more easily, increasingly happen by habit, automatically. As such, I can see how eventually I might be tempted to say "I want/choose to brush my teeth" even though I very much dislike doing that. I can also see how I might say "I have to brush my teeth", especially when I am relating that to context, eg when stressing that, say, I can't go to bed just yet, because there's still this one item left to do on my agenda.
But even at that point, I don't see myself as saying "I desire to brush my teeth". For me, that would be just as weird as saying "I desire to go to work tomorrow" even though I really don't. What I desire is shelter and orange juice. And toothpaste, I guess
If I wasn't so painstakingly clear about what it is that I desire, my entire behaviour and daily structure will soon be fragile again, prone to collapse, subject to both internal and external sources of corrosion. When I get sloppy with what I desire, the only sensible desires which continue to prevail are natural, necessary and immediate ones: food, water, sleep and shelter, but not even showering, doing dishes, or airing out the flat, and more abstract, more indirect things like work completely fly out the window anyway.
My point in saying this is not to whine or get a pat on the back; my point is that while the extend of this effect is a bit extreme in me, I am quite certain the underlying mechanics are the same for everyone. Therefore, when faced with a lack of drive, energy, motivation, consistency, structure, discipline, …, everyone might benefit from being extra clear to themselves about what it is they desire.
That might just do the trick.