Is there any game that is in the gambling industry that is not for luck? As for me all games have the element of luck. Look at these skill games golf game, poker game, Bridge game, Car race, Motor GP (Sport) game, Gin Rummy. The above mentioned games are purely skill games but there is and element of luck to win the games. And when you lose any of the games, you would say eh! I don't have luck today. Slot games are purely for lucky games, but you don't have to tactically depends on the luck but do well and depends on the faith to win the game. Yes as you said, hoping to win at all time will be disappointing.so you only play the ones you can do well. In some cases gamblers have confidence to win the game though it happens but not at all time.
There is no gambling game where luck is not an important element. If we have more knowledge about some sports, or we are skilled at some card games we will have higher chances of winning, but without luck in the "last seconds", or on the "river" it is very possible that we will lose more than we will win.
In my opinion, slots are a special category... we depend only on luck, and it's interesting to spin and wait for the bonus round and some huge win. Slots can give a lot and be very generous, but they can take even more if we are not careful with the base bet/bankroll ratio. When it comes to bonus buys, we can just press the buy bonus button and hope for the best... there are no strategies we can apply, it's pure gambling and luck.