HMmmm ... since I have never deposited on any poker site
and have BR's on the sites I do play on, can't say I've really 'lost' anything due to one single cause.
What I do find is that I lose some 'hands' for 2 reasons ... 1) making a mistake in a specific situation - and hopefully learning from it, and 2) losing a hand in the odds
percentage that I 'SHOULD' lose. My AA 'WILL' take a beating ... sometimes.
But if you're making good decisions, your loses will be small and your mistakes very identifiable.