>Doublejack is a must buy.
>Chapel is a must-buy.
>Mountebank is a must-buy.
>Sea hag is a must-buy.
>etc...
The reason I hit a wall at rank 30 (I'm currently at 37) was that I believed that there were rules about which cards were good when, and it all came down to counting terminals. Absolutely everything you know about whether a card is good or bad is wrong in some situation. Remember ALWAYS to think about cards as their effects on your hand, your deck, your opponent, and your score.
>If I had terribly bad luck at turn 3 or turn 4, I've lost.
Sometimes games suck and deserve ragequits, but if you have less than 9 curses, aren't getting ghost-shipped every turn, or multi-possessed without the ability to self-sabotage properly, there's a good possibility you have some chance. If it's a one-time occurrence, luck can even out over the turns.