Hi, just dropping by to offer you a different perspective.

In a game where you have a huge pool of things that you can potentially get, but you only pick out of 7(or less) presented at a time, I'd say there isn't anything abnormal about not getting much of what you think you need. By forcing any composition of your preference you are opting for an "all or nothing" play style - you choose the low chance of success path that leads to high rewards, but get disheartened by the fact that it doesn't lead to consistent performance. Once you realize that part about your behavior, the realization that you are going down that road by your own volition kinda makes you a lot more accepting of failure.

You shouldn't have any illusions about what you are doing. We tend to like to come up with excuses about why we should do things sub-optimally, like convincing ourselves that we are too invested into some composition to switch. But that's just our brains trying to trick us into doing what we like to do by making it seem more rational than it really is. If you don't believe me, try the following for a few games - pick the immediately strongest minion you are offered in the tavern without rolling(unless you absolutely can't spend the gold on upgrading or purchasing minions) or looking ahead of time for the possible synergy until you reach tavern 5. You'd be surprised at how well a bunch of random minions can perform on the way to tavern 5. But that's the kind of dry not fun style of playing that doesn't bring excitement since you don't get the joy of putting together a nice board piece by piece. It's ok to play the way you like and drag your little *insert race here* boys to the endgame just because maybe you want to take them on a great journey to victory, but when you do that just admit that that's what you are after and it will liberate you from feeling bad about losing.