There are some things you learn the hard way. Like whenever a particular event occurs, you feel like a success, like your life has meaning, but then you forget about it and think that you'll never feel like that again. You have to remind yourself and trust that even though it doesn't feel like it right now, the technique works - and it works regardless of what you feel at any given moment.
You need to take the chance and try recreating the event, even if you don't feel like it would work. Because what's the other option? That you don't try it, and just wait for some other technique to come save your day?
There's a common denominator between the happiest memories of your life. Figure it out, and create more events that include that denominator. Sooner or later your mind will begin to trust the process.
Same goes for negative memories. Scan your mind for some of the most recent bad memories or events when you felt terrible. Is there a common denominator? Was that denominator something you could affect in the future? Make a mental note. I get that you have little influence over the health of your loved ones, and a family member's death is something you can't exactly affect in the future, but think about the events that happen more or less with you alone. Did you control your emotions poorly? Did you hurt someone? Did you eat something you shouldn't have?
Life is suffering, and while I'm not a hedonist, I certainly think that unnecessary additions to that fundamental suffering are, well, unnecessary. Unless you're trapped in a forced labor camp and can find meaning in suffering. Or unless you want to make your life hard as a way of punishing yourself - in which case I suggest you analyze whether beating yourself up really is as beneficial to your mind as you think.
As long as you're not making anyone else's life harder, I really don't see any reason why you shouldn't try to increase the happiness or meaningfulness in your life.