The pattern is the same every time. I get a ~50-100g packet of some black or oolong tea. The first time I open it, the aroma is great, the taste is amazing- I say to myself, "This is it. This is my tea." Around 1-10 sessions later, I open the tea and it has no aroma. I brew it, and there's almost no taste. This last was the worst- admittedly, it was just a TGY from TenRen, but after drinking it for two weeks and really enjoying it, I took a break for a week, opened it, and it had literally no aroma, and even with ~5g in a 50ml gaiwan for 30+ seconds I almost couldn't distinguish its taste from the water I used (I tested this).
-I don't think it's the type of tea, because this happens pretty much anything I buy;
-or the quality of tea, because this happens with tea from well-regarded online vendors and tea from my local Chinatown. (and honestly, if I have to pay premium to get, not something that tastes great, but something that tastes *at all*, this isn't the hobby for me)
-or what the tea is stored in, because this has happened with tea kept in the same airtight, lined bag it came in; in plastic ziploc bags; in tins; and stored open in a cake (some yunnan black and yue guang bai, and I know that was a mistake);
-or where in the house it's stored, because this happens whether the tea is sitting on my desk, in a bin on the floor, or stored away in a dark closet, in all cases with nothing else fragrant nearby except other (sealed) tea; and whether it's on the first or second floor;*
-or the water or general climate, because this has happened in three cities in the Midwest USA and in Belgium, in every season;
-or the brewing parameters, because I've tried everything with every tea that goes stale, almost always to no avail; and when I overbrew the tea it gets uncomfortable and gross but still with no real taste, not even bitterness, really;
-or me imagining tea should be stronger than it is, because this tea starts *very* strong, and ends tasting like plain water (and I'm not a coffee drinker

*One possible exception to storage: the last, terrific failure seems to have happened a week after I put some unsealed tea bags, a gift from a family member, in the same cupboard. These bags are almost odorless themselves, and the affected tea was in an airtight tin, but could it still have done it? Still doesn't solve my general problem, though.
I'm tired of buying 100g of tea and getting max 50g, usually 10-20g out of it. Sorry for being grumpy, but this has been going on for a couple years and I'm close to giving up. Is there anything I could be missing? Could it just be a string of unconnected newbie failures, like putting the tea bags in the same container this last time? I know I have stored tea very badly in the past, and suffered for it, but I've left those instances out of the equation.