Why I can't break 800 elo on 30 rapid chess.

So I will be doing good making fairly good moves winning/drawing against most players below 800 elo. Then, just when I think I may break into 800, my hopes are instantly crushed when I think so hard on a move and miss a checkmate 4 moves into the game. 😩 😂😂😂 I guess I just need to go back to the 3 day games. I don't think well under pressure. Question is, will I ever get good enough to play at a faster pace? I don't think it's possible for me. So if anyone wants to play a 3 day game with me I would appreciate it. Also, if you go look at my profile, you will see I haven't done many puzzles. I have other means for that besides this website. I mainly like doing drills over puzzles anyways. Thanks for taking the time to read my discussion of my poor play. Cheers!😁

No, you will get better! Keep on practicing. As you mentioned at that level everything comes down to tactics and hanging pieces. Perhaps a change in perspective will help. Before making moves are you considering both your and your opponents threats/ideas? Good luck with your chess!