So far, there's not a list that shows what the requirements are. At the conversion, many of us got several cards in a series all at once, because we had met all the requirements.
So far, what is known is that the "Mood Loser" cards appear in your deck the following times;
Mood Loser I, when your energy tank goes above 600
Mood Loser II, when your energy tank goes above 1200
Mood Loser III, when your energy tank goes above 2000
In general, the first of the cards will appear once you have completed the skill that they apply to.
I think the system's not done. And they're kind of forgetful at times, or don't notice things that seem obvious to us. By pointing out that some system for communicating the requirements for cards is needed, you've already done a lot to put that idea on the devs radar!
I'd suggest making an ideas post. Even from my observations and actions (I've bought all the cards I can) I haven't been able to puzzle out what makes half the cards show up.
EDIT: Perhaps there's an encyclopedia section for cards coming up someday soon? If not, that'd be another idea worth putting in the ideas forum. I should really post more of those xD
EDIT2: To actually answer your question, I don't think they ought to be secrets! I agree! And second, I don't know what they think, but I can tell you what I think ;) I don't think it helps gameplay at all. And I would advocate a reference that would tell us these things so we can make informed gameplay decisions.
@MomDressU:
Liza Throttlebottom was not disparaging the OP's question. She was merely suggesting that if it hasn't been done, a posting in the Ideas forum might alert the devs to the need for the explanatory material the OP was seeking. Her point was the information is not available because the devs may not be finished creating it. That's all. I think we are all sympathetic to the OP's question and have wondered the same.
Lots of mechanisms have been left for players to explore - iMG caps, amount of favor from donating, number of animals that can live in a street, locations not listed in encyclopedia, etc.
Sometimes this generates a great social effort to get to the bottom of things, which may be great fun. Other times you just wanna know.
@Togger Yeah, I'd put my vote in for this being something you just want to know. The randomness factor of the cards can be fun, but some sort of reference from the devs, similar to the skill page we have now, that shows us which cards we have now, what cards there are, and how to get them would be swell. As it is there's simply no way to know whether things are working the way the devs want them to.
I think the devs had said that cards will eventually be put into the encyclopedia, though they didn't say whether it would tell requirements or not. I don't remember which dev or where that statement was, but I might look for it later.
ETA: Also, I do think most cards would benefit having the requirements told, though I think some could be fun to not know. Sorta like hidden achievements.
"They" don't want the requirements to be a secret (indeed, they want the information to be available to all players) and neither are they forgetful or oblivious to the obvious things like this: they just have a lot of different things to do and have to chose some kind of order in which to do all those things which is based on the importance of each thing, the urgency of each thing, the complexity/amount of effort in each thing and the availability of various people in each of the many disciplines/domains which go into pushing as single new thing out :)
Sorry Stoot, I didn't caveat that statement very well :( The idea I was actually trying to convey was that the devs are human and can't think of EVERYTHING. This wasn't such a good example, as it was found that you'd already said something like this was on its way, but I've heard other staff members say that we should always post all of our ideas, as sometimes players are just looking at things from a different perspective.
Oh, you are definitely encouraged to post ideas — it's definitely helpful and every once in a while someone comes up with a much easier or more elegant way to accomplish something which we've been wanting to do.